A neural network is just a machine made of little knobs. It makes a guess, sees how wrong it was, then sends that mistake backwards to nudge every knob a tiny bit. Do that thousands of times and the machine teaches itself — here, to solve XOR.
Watch one guess flow forward through the circuit, see how wrong it is, then watch the blame flow backward and turn the knobs. Press Step once to go slow, or Train to let it teach itself. Make the steps too big and you'll see the brain break — then fix it.
Colours: teal wire = a knob that adds · red wire = a knob that subtracts · thicker = stronger. The green dots are the guess flowing forward; the red dots are the blame flowing back. Keys: S step · T train · N new brain · R reset · ← → slides.