Discovery of penicillin
In 1928 Alexander Fleming came back from holiday to find his lab had been working harder than he had.
Fall of the Western Roman Empire
The Western Roman Empire is said to have fallen in 476 AD, though it mostly sat down slowly.
Goose
A goose is a large water bird; its plural is geese, its male is a gander, and its opinion of you is low.
Parallelogram
A parallelogram is a rectangle that has been leaned on, and its opposite sides have never met.
Nanosecond
A nanosecond is far too short to do anything in, so nobody has ever been late within one.
Cul-de-sac
A cul-de-sac is a street with only one end, which it uses for both arriving and leaving.
Pine cone
Pine cones open in dry weather and close in wet weather, making them nature’s way of not looking outside.
Whirlpool
A whirlpool is water that normally goes along deciding to go around instead, usually without warning.
Stapler
A stapler always knows how many staples are left, and keeps it to itself until the answer is none.
Custard
Custard is poured over puddings and is itself a pudding, so it can be served on top of itself.