A snack break by accident revealed a new class of brain cell

Researchers recording a single neuron in a macaque's brain noticed it fired not only when the monkey grabbed a peanut, but also when it merely watched a researcher grab one. The accidental discovery of these 'mirror neurons' reshaped theories of empathy, imitation and how we read others' actions.

— Giacomo Rizzolatti et al., Action recognition in the premotor cortex — Brain, 1996