Ken Kahn's Ani (MIT, 1978), running again
On Ani's Cinderella, learners watch a film made in 1978 by an AI program, ask any character why it does what it does, change the story, and compare Ani's way of thinking with today's language models. This guide has session plans, printable activity cards, discussion questions and practical notes for classrooms, libraries and university courses.
Ani is the program in Ken Kahn's MIT PhD thesis (1979), which he rewrote substantially as the technical report AI-TR-540. Given a short description of a story, it reasons its way to an animated film of moving shapes, and records why it made every choice. The film page runs Ken's 1978 program again, in the browser, so learners can question it, change the story and see what Ani does.
A good thing to watch first: Ken's 1978 film of Cinderella on YouTube, or a new version made by the site's app, with subtitles and Ken's 1978 narration, cleaned up.
The guide for students has the same activities, numbered the same way, written for learners, with the answers behind What to look for.
How AI was done at the MIT AI Lab in the 1970s: knowledge written by hand, reasoning with symbols, programs built from “actors” that send each other messages. The page runs Ani's actual 1978 code, recovered from the lab's backup tapes, on a MacLisp interpreter rebuilt for the revival: not an imitation of it.
Ani reasons from knowledge Ken wrote by hand; a language model writes from patterns learned from vast amounts of text. On this page they work together (a model can turn a story into Ani's notation, and Ani does the rest), so students meet both in one task and can see what each is good and bad at.
Ken called Ani a “glass box”. Every choice comes with its reasons: the chain from an action up to what the story asked for, the alternatives weighed and their scores, the suggestions kept and set aside, down to the line of code. Students learn what makes an explanation checkable, and how that differs from a model explaining itself after the fact.
Predict, run, compare. Change one word and see what changes; find where Ani stops on a new story, read why, and see what the revival's repairs do about it. These are the habits of anyone who builds or tests software, and of scientists running experiments.
Ani's characters never speak. Personality, feelings and relationships are shown only by how shapes move: fast or slow, straight or curvy, toward someone or away. Students see what a story needs to say, and what a storyteller (or a program) has to invent.
No programming is needed. Knowing the Cinderella story helps. Some of the page's text is dense, written for adults: the first line or two of each panel are the important part, and the rest is there on a click.
| Who | Suggested activities | Notes |
|---|---|---|
| 10 to 12 | Start here, cards 1 to 6, in pairs | An adult reads the first lines of the side panel aloud with them. Skip the Lisp. Card 5 (a kind stepmother) is the highlight. |
| 13 to 16 | All of Start here; most of Going further | Hard challenges for keen students. A new story with a model (card 8) works well as a whole-class activity. |
| 16 and up, and university | Everything, with AI-TR-540 and the code pages | Good for courses on AI history, knowledge representation, explainable AI, or computational creativity. |
| Option | Cost | What leaves the computer | Good for |
|---|---|---|---|
| Gemini Nano, built into Chrome | Free | Nothing | Children's workshops. It needs desktop Chrome on a computer that can run it, and the first use downloads the model (a few gigabytes), so do that before the session on each computer. Its drafts are rougher. |
| Claude, ChatGPT or Gemini with an API key | Paid by whoever owns the key | The story and Ani's instructions, sent from the page straight to that company | The best drafts. Run it on the teacher's computer, on the projector. |
| The claude.ai copy of the page | Each person's own claude.ai account | The story, to Anthropic through claude.ai | Adults who already use claude.ai, such as university students: no key at all. |
An API key works like a password, and whoever has it can spend money on its owner's account.
The site has a copy of the page made to run inside claude.ai: ani-cinderella-claude-artifact.html. Upload it to a claude.ai chat and ask Claude to copy it, exactly as it is, into an HTML artifact. There, Tell Ani a new story offers Claude on the viewer's own claude.ai account, with no key (claude.ai asks the first time), and Gemini Nano.
claude.ai accounts are for adults, so this is not the route for children's workshops.
The page carries everything it needs. Once it has loaded, watching the film, asking why and making films all happen in the browser, with no internet. You can also save the page (Ctrl+S, “Webpage, HTML only”) and open the saved file later; save Ani's Choice Points and Ani's Code in the same folder if you want their links to work. Without the internet the page uses plain fonts, and only Gemini Nano, once downloaded, can tell new stories.
Card numbers refer to the activity cards below and in the students' guide. Films take a few minutes to make, so start one, then do something else while Ani works.
| Time | What happens | Notes |
|---|---|---|
| 0–5 | Hook. Play The Introduction on the projector without explaining anything (or the start of the narrated film, or of Ken's 1978 film). Ask: who's the villain? How can you tell? | Movement alone tells them a lot. |
| 5–10 | Reveal. A program made this in 1978, from a short description. Show What Ani was told. | Ani isn't a chatbot: it reasons from knowledge Ken wrote, and records why. |
| 10–20 | Pairs: cards 1, 2 and 3. | Card 3 is the “aha”: the description never says “push”. |
| 20–25 | Predict. What will a kind stepmother change? Write predictions on the board, then start card 5 on the projector computer (or on every computer). | At 4 a second, two to three minutes. Keep the tab in front. |
| 25–35 | While Ani works: card 4. Then watch the two films side by side and check the predictions. | The kind stepmother still stands guard in Kept Apart. Ask why. |
| 35–45 | Card 6, then the discussion: Ani explains every choice. Can a chatbot? | See the discussion questions below. |
| 45–55 | Optional: tell Ani a new story together (card 8) on the projector. | Gemini Nano, or your key on your computer. |
| 55–60 | Exit: each person finishes the sentence Ani knew … but didn't know … |
| Part | Activities | Outcome |
|---|---|---|
| 1. Watch and ask why | Cards 1 to 4; the words to know at the end of the students' guide | Students can find and explain one of Ani's choices from the glass box. |
| 2. Change the story | Cards 5, 6, 7, 12 and 13; start one film at the beginning so it is ready halfway through | Students predict the effect of a change, test it, and explain the differences. |
| 3. New stories and today's AI | Cards 8 to 11; one hard challenge; discussion; a short write-up | Students compare what the language model and Ani each did, and where and why Ani stopped. |
Each card says what students do, what they should find, and what to watch for. The students' guide has the same activities in learners' words.
Watch The Introduction without reading anything, then describe each character from how it moves.
The square (the stepmother) rushes at the star (Cinderella) and shoves it, five times, then chases and hits it; at the end the star and the triangle (the Prince) travel together. Personality and relationships come across without a word.
Students reading the side panel first. Ask them to just watch.
Read What Ani was told, then Show it as Ani read it. Name three things the film shows that the description doesn't mention.
The description has the characters' words, how they feel about each other, and five scenes, each with tasks and a mood, rhythm and length. It never says where anyone stands, how fast they go or what they do: Ani decides all of that.
The Lisp can put younger learners off. It's optional.
Pause The Introduction while the square pushes the star, click the square and open Why.
The chain of reasons: she pushes Cinderella around to establish that she dominates and hates her, as the film description asks
. The word “push” is nowhere in the description: pushing is Ani's way of showing that relationship. Why so long: the push repeats five times because Ken's code for it says so, and the scene is meant to be long, 30 to 75 seconds.
Clicks that miss the shape. The ◂ and ▸ buttons step one frame at a time.
Find the stillness near the end of The Meeting, at 24 a second, or the slanted no one moves
line in The Meeting, part by part. Click it, and open Why no one moves.
About six seconds where nothing moves. The last part is only feelings (Cinderella and the Prince are very happy); Ani shows feelings by changing how characters move, but no one is moving, so nothing shows. AI-TR-540 says such changes cannot stand alone
(p. 125). With the revival's extensions (SEEN), the two wander about instead.
At 4 a second the pause is under two seconds and easy to miss: use 24.
Write down three predictions. Change the story, A kind stepmother, Make the film; then watch side by side.
Made by Ani as in 1978, 21 of the 102 choices of how the characters move come out differently (the stepmother is slower and less deliberate, and now likes others). In The Introduction she no longer pushes and hits Cinderella; she goes to her and keeps her company. But in Kept Apart she still stands guard: the scene's tasks, which weren't changed, say she prevents the meeting. Character words change how characters move; the plot lives in the scenes. (At 4 a second, the fairy godmother also stands guard in No Longer Kept Apart, keeping the stepmother away.)
Tabs left in the background: Chrome slows them. Give waiting students card 4 or 6 to do.
Open Change the story and read the notes under the word lists before changing anything.
Ken's own story has the fairy godmother is protective of
Cinderella; Ani knows only “is protective to”, so the word is remembered but suggests nothing. And “strong”, a word for personality, is given as the Prince's looks. Neither stopped Ani in 1978.
A good bridge to discussion: should a program stop when it meets something it doesn't understand, or carry on quietly?
Click the triangle at the end of The Introduction (the description of that scene names only Cinderella and the stepmother), then Cinderella, and open Why.
Cinderella goes to the Prince and goes along with him to establish what Cinderella is like
. To show a trait, Ani may need someone to show it with, and brings them in.
A chance to talk about inference: Ani adds what the description implies but never says.
Tell Ani a new story; a ready-made story (Red Riding Hood, The Tortoise and the Hare, Beauty and the Beast) or their own; Write the film description; read the result before making the film.
The description in plain words; notes where the page tidied it; any problems Ani's checks found, with a button to ask the model to fix them; and differences from the story they told. Ani can show only what characters are like, how they feel and what they do to each other, so talking, objects and places have to become chases, guarding, rescues and feelings.
Models inventing characters, or making a prize or a place into a character. That is worth discussing, not just fixing. Simple stories of a few characters who love, hate, chase, guard and rescue work best.
Make a new story with Ani as in 1978. If it stops, read Where Ani as in 1978 stopped and What Lisp said; then Make it again with the revival's extensions.
A plain-English reason for each stop, with the 1978 program's own message. For example, a tortoise-and-hare story stopped because nothing suggested how active the hare should be, so pass 1 gave up on it and pass 2 couldn't go on. Made again, the side panel says what each repair did.
Students treating a stop as the page breaking. It is Ani as Ken left it, meeting a story he never gave it.
Make Ken's story, unchanged, with Ani with the revival's extensions; read Which extensions; compare with Ken's film.
None of the 102 choices of how they move change, but Ani now draws the characters itself (at the time of writing, Cinderella as a small purple hexagon and the Prince as a large red circle, for example) and says why. The Introduction gains new parts (Cinderella helps the Prince along, and follows her stepmother), and at the end of The Meeting the two wander instead of standing still.
The question underneath: if new code is written in Ken's style from his own ideas, whose program is it?
Change the story, Cinderella beautified, make the film; watch the new scene; click Cinderella in the scenes after it.
Ken wrote this scene in 1978 and left it commented out. Made with the extensions, the fairy godmother goes to Cinderella and transforms her at once (she is magical: the revival's rule); then Ani takes a fresh look at Cinderella as if the character were brand new
(AI-TR-540, p. 168), and the side panel says how she has changed.
It needs the extensions; the page switches to them for this scene.
Watch a scene at 24 a second, then at 4, and find differences; then compare a film of their own with Ken's, side by side.
The two rates are two different runs: even The Introduction is filmed differently (about 38 seconds at 24, about 48 at 4), and each later scene is planned from where the last one's filming left the characters. 24 is the rate of Ken's camera; 4, of his TV previews and the flipbook printed in AI-TR-540.
A good moment to ask what “the” film is, when one program and one story give two.
Open Ani's Choice Points, read the stepmother's speed (As the thesis tells it), then explore others.
The stepmother's speed (high) was decided at attempt 825 of 836, after 10 postponements. The four characters' speeds wait on one another until the film's focus breaks the deadlock. Ken walks through this choice on pp. 20–23 of AI-TR-540.
The table is dense. Point students at one cell at a time.
Each depends on what Ani actually does, which is found only by running it, so a frontier AI model asked the same question usually gets it wrong too. Have students record a prediction before they check, and let them compare a chatbot's predictions with theirs.
Each opens on a click to what to listen for.
Listen for the difference between a record of the reasons a program actually used and a plausible explanation written afterward. Ani's reasons can be checked against its code; a model's explanation of itself is more text it generated. But Ani's explanations are only as good as Ken's rules, and a model can explain many things Ani never could.
The page tells the language model that Ani can't show places, objects, races, winning or speech
, so a win becomes the winner's joy and pride and the loser's shame. AI-TR-540 says Ani cannot handle very concrete expressions such as “a glass slipper”
(p. 19). Listen for: Ani knows characters, feelings, relationships and movement, nothing else; winning needs a race, rules and a finish line. What would Ani need to know to show it?
Ken asked it himself: who really made the Cinderella film — Ani or me?
(p. 207). His answer is that it is a matter of degree: how many levels of reasoning, how many choices, how much knowledge. Extend it: who made a film from a student's story, told by a language model, planned by Ani, with repairs written in 2026?
Ken lists the objections, among them Ani only does what it's told, humans only sometimes do
(p. 209), and then argues against them: Ani has rules for when to follow, change or reject its own suggestions, and breaks them often (pp. 210–211). Students can find examples in the glass box: suggestions set aside.
Listen for the idea that the description has two parts, the characters and the scenes, and that changing one doesn't rewrite the other. Is a stepmother who is kind but still stands guard a contradiction, or a more interesting character?
Listen for: it depends what's at stake. A stop is honest but unhelpful; a confident answer is helpful but can be wrong. Ani also carries on quietly in places (the word it doesn't know in Ken's own story): is that better or worse than stopping?
The extensions are new Lisp, written in Ken's style from ideas in AI-TR-540, in files of their own. Ken's 1978 film is always shown as it was made. Is a repaired Ani the same program? (A version of the Ship of Theseus.)
Listen for bias (whose ideas of “evil” or “graceful”?), for mistakes and who can find and fix them, and for who is responsible for what the program does.
From AI-TR-540; the page numbers here and throughout this guide are its.
Ani is built upon the principle that as few decisions as possible be determined arbitrarily.Ken Kahn, AI-TR-540, p. 22
Difficult choices are postponed to be resumed when more of the film has been determined.p. 2
The essence of animation is change.p. 168
Ani is a creative entity that is a “glass box” that we can look inside …p. 208
… one can learn much from a relatively simple model of a complex process because of its very simplicity.p. 13
| Level | What it looks like |
|---|---|
| Describes | Says what happens in the film, or what changed. |
| Explains with evidence | Says why, quoting Ani's reasons from the page. |
| Explains and generalizes | Uses the evidence to say something about how Ani works, what it knows, or how it differs from people or from language models. |
Keep its tab in front: Chrome slows tabs in the background, and the status line above the film says when Chrome has paused it. At 4 frames a second a film takes two to three minutes on a recent computer, about five with Ken's beautified scene, and about a quarter of an hour at 24. Each scene plays as soon as it is filmed. Stop, beside the status line, ends the run.
That is Ani as Ken left it, meeting a story he never gave it. The side panel says where and why, in plain words, with what Lisp said a click away. Make it again with the revival's extensions usually gets further. Stops make good discussion (card 9).
Read the plain-words summary before making the film. Ask the model to fix the problems the page lists, try a stronger model, or open the description in the editor (Look it over, then make the film) and change it there. Small models such as Gemini Nano write rougher drafts. Short, simple stories work best.
It is built into recent desktop Chrome, on computers that can run it, and downloads the first time it is used (a few gigabytes). If it isn't offered, that computer or browser can't run it; use a key on the teacher's computer instead.
Check that the key is for the provider chosen (Claude needs an Anthropic key, ChatGPT an OpenAI key, Gemini a Google AI key), that the account has credit, and that the model chosen is available to it. The page shows the provider's message.
Made with the revival's extensions, Ani chooses each character's shape, size and colors itself (APPEAR), and the side panel says why. Ken's 1978 film is always drawn as Ken drew it.
The page keeps films in the browser that made them. A private or guest window, a different computer, or clearing the browser's data loses them. To keep a film, use Save: a film file opens on the page again later, with all of Ani's reasons; a video plays anywhere.
What the page keeps. In the browser on that computer only: settings (the frame rate, TV or color, which Ani and which extensions, which model), the story being told, the description being edited, and the films made there, so they are still there after a reload. API keys are kept only if Remember keys in this browser is ticked. Nothing is kept on a server. On shared computers, a Chrome guest window forgets everything when it closes; otherwise clear the site's data afterwards.
What leaves the computer. Nothing about the stories, unless someone:
Loading the site fetches its fonts from Google Fonts. And on the site, if something goes wrong in the page, an error report goes to Ken through Sentry, an error-reporting service, so that he can fix it, without any story, key or personal data, as the film page's footer says.
Children. Ask them not to put real names, addresses or other personal details into stories. Model providers' terms have age limits and claude.ai accounts are for adults, so with children use Gemini Nano or your own key on your own computer.
Content. Ani's films are abstract shapes; in Ken's Cinderella the stepmother pushes and hits Cinderella, shown as shapes bumping. Language models can write unexpected things; the page shows the description in plain words before Ani films it.
cannot stand alone(pp. 125–126); characters who change (pp. 168–169); Ani and creativity (pp. 205–212); the Cinderella film description (Appendix I).