Pick two animals to defend you. A simulator and its history.

You've probably seen this.

You're in an arena with: 50 hawks, 10 crocodiles, 3 brown bears, 15 wolves, 1 hunter with a rifle, 7 buffalo, 10,000 rats, 5 gorillas, 4 lions. Pick 2 to defend you. The others attack you. Goal is to survive 1 hour.

It comes round every year or two, and every time it starts the same argument. Somebody says rats, because 10,000 of anything wins. Somebody else says the hunter, because you don't want the only gun pointed at you. Then someone insists the gorillas would deal with the hawks.

Every time, I've thought someone should just simulate it. Model the animals, run it a few hundred times and see who's still standing. I never had a spare evening to build it.

I saw it again on Monday, and this time, rather than adding it to the someday list, I handed it to Claude.

What I actually did

I gave Claude Code a prompt asking for a browser-based simulator of the thought experiment (pasted in verbatim), with a screen to pick your two, a full-screen view of the fight and no server-side code.

Claude came back with four questions:

Realism, grounded or arcade? I said configurable.
What's the arena like? Open dirt with a pond.
Do I steer, or just watch? Just watch.
Watch one run, or lots? Run 100, then replay one.

That was nearly all my input. Claude wrote the engine, built the interface, tested it in a browser, tuned the balance over several passes and wrote the README. Later I asked for the code on GitHub and the site on Cloudflare, and it did both.

There are four ways to use it:

Watch the hour from above, as animals circle, hesitate, charge, block, run off injured and stop to eat what they've killed.
Run 100 trials and get your survival rate, what killed you and when.
Rank all 36 possible pairs.
Tune any animal's stats and see whether the answer changes.

Try it here: https://animal-arena.marcroberts.info

So what should you pick?

Under the default settings, take the buffalo. The 7 buffalo are the biggest lump of health and bulk in the arena, and they're also the deadliest attacker, killing you in most of the runs where you don't pick them. Picking them takes your biggest threat off the board and gives you something large to hide behind. Pair them with the crocodiles or the lions and you survive every run.

If you don't fancy the buffalo, take the rats. Bears and rats survived 96% of runs.

The hunter is a trap pick. As an attacker they rarely get a clear shot before something fast runs them down, and as a defender one rifle doesn't stop 4 lions arriving at once.

All of this is judgement calls written as code (largely Claude's), and I'm no zoologist. If you disagree, open the Tune panel, change the numbers and re-run it.

Where did this come from?

While writing this up I wanted to credit whoever started it. The earliest version I'd seen was a tweet from Sahil Bloom in early 2023, so I asked Claude to dig further back. It goes back a lot further than I expected.

2023: the hawks, buffalo and "hunter w/ rifle" version does the rounds on Twitter. That's the one I remember.
July 2022: Know Your Meme already has an image, with the note "No idea who's the original author."
July 2020: it went viral on Twitter, and coverage at the time said it "has circulated for some time".
25–26 January 2018: Vice published "This Meme Broke Our Office", Barstool's KFC Radio did an episode on it, and forums like ResetERA had threads going.
Before that: Reddit's r/whowouldwin had been running the same format with fictional characters through 2017 ("pick 3 to defend you, the rest try to kill you").

That's as far back as I can find. Every early source says it came from "somewhere on the internet", and one forum reply mentions an "original Reddit post" I couldn't track down. If you know who made that January 2018 image, I'd love to credit them.

Why I finally built it

I've had this idea for years and could've built it myself, I just couldn't justify a weekend on a toy. This time my part was a few minutes answering questions, and Claude did the rest (it worked away for about three hours). A lot more of my someday list looks worth doing now.

Which two would you pick? Run it and let me know whether the simulator agrees with you.

The code's on GitHub: github.com/marcroberts/animal-arena