Special exhibit · on loan from one real animal
Sneak Up On This Brain
Through that door is a fruit fly's escape circuit: six hundred and sixty-eight neurons, wired to each other exactly the way they were wired in life, running live in your browser. Your cursor plays the predator. Creep in slowly and it will ignore you completely. Lunge, and it is already gone.
You will not beat it. That isn't the exhibit. The exhibit is why you can't -- an answer that takes about four thousandths of a second and involves no thinking of any kind.
Give it a moment to open -- there are a lot of neurons. Sound is optional and worth it. The room is dark; the rest of the museum will still be here.
Afterwards
Everything structural in that room is measured, not invented. Which neurons exist, which one connects to which, how many synapses each connection has, whether it pushes or pulls, and where every cell body sits in space -- all of it read off an actual brain by FlyWire, the first complete wiring diagram of an adult animal. What is added is the physics: each neuron is modelled as a simple leaky integrator, and your cursor is converted into the shape of an approaching thing. The decision to flee you is then made by the measured synapses, not by any line of code that knows a cursor exists.
Two details the room itself is too polite to dwell on.
The first is that it is not "a fly." It is the fly. That wiring came from one individual seven-day-old female Drosophila melanogaster, killed, set in resin, sliced into thousands of sections and photographed under an electron microscope. Then traced -- cell by cell, over years, by machine learning and by several thousand humans arguing about where one neuron ended and the next began. She has no name. She is the most completely known animal that has ever lived, and a fragment of her is now running on your laptop because you moved a mouse.
The second is that you have one too. Looming detection -- the machinery that turns object getting bigger, fast into move -- is such a good idea that evolution has found it over and over in unrelated lineages. A zebrafish has a single enormous Mauthner cell doing very nearly what her Giant Fiber does. Yours is wired through your midbrain, and it is the reason your hand comes up before you have decided anything. Every flinch you have ever had is this exhibit, running on you.
So: is anybody in there? The honest answer is that the room is not equipped to ask. What is running is roughly half of one per cent of her brain -- one reflex arc, lifted out and kept alive on a bench. Even if the whole fly were in there, we would still have no agreed way to check, which is the problem the rest of this museum is about. What this room can tell you, with unusual confidence for these premises, is something smaller and stranger and completely true: a decision is being made, it is being made out of measured biology rather than storytelling, and it is beating you.
Provenance. Connectome data: FlyWire (Dorkenwald et al. and Schlegel et al., Nature, 2024), dataset FAFB v783, released under CC BY-NC 4.0 -- non-commercial, which this museum has always been and intends to stay. The simulation is ported from the open-source DesktopFly project: same circuit, same constants, same test invariants. It is a guest here and keeps its own house style. The full story of the scan -- the diamond knife, the custom camera, the 33 person-years of tracing, with pictures from the microscope -- is at the bottom of the dark room, for the really curious.