In 1780, Luigi Galvani discovered that when you put electrical current through a severed frog leg, it’d twitch. This would eventually lead to the development of the Galvanometer.

A mechanical device containing two electrical connectors — one black, one red — and an analog readout dial.
A Peaktech 205-08 analog galvanometer.

Hence imagine you are doing some home improvement, and want to verify whether a wire is live. But alas, you don’t have a galvanometer handy – and while you could turn off the power mains, well, that’s too much trouble.

How about using a test light? Alas! You don’t have one and the stores are closed…

A yellow screwdriver-style test light being inserted into a power socket. The test light inside the screw driver is lit up.
A test light. Yep, that one’s live.

Instead! Head to the nearest pond, and catch yourself a frog. Or even better, catch yourself a few, because you’ll need to replace your frog’s leg galvanoscope every two days…

An ink drawing of a test tube containing a severed frog leg. The top of the frog leg has a thin metal wire sticking out of it.
A frog’s leg galvanoscope.