A chimp named Sultan solved a problem by suddenly 'getting it,' not by trial and error

Wolfgang Kohler gave chimpanzees a banana just out of reach, with sticks and crates scattered around the cage. Instead of blind trial and error, the chimps would pause, then suddenly assemble a solution, stacking crates or joining sticks, as if a lightbulb had gone on. Kohler called it insight: a sudden mental restructuring, not gradual trial-and-error learning.

— Wolfgang Kohler, The Mentality of Apes — Kegan Paul, 1925 (English translation)