A mouse finds itself in a box it’s seen before; inside, its white walls are bright and clean. Then, a door opens. On the other side, a dark chamber awaits. The mouse should be afraid. Stepping into the shadows means certain shock — 50 hertz to the paws, a zap the animal was unfortunate enough to have experienced just the day before. But when the door slides open this time, there is no freezing, no added caution. The mouse walks right in.