Did twitching frog legs prove animal electricity, or only two different metals?

Both, in a way. Luigi Galvani found in 1780 that the muscles of dead frogs' legs twitched when struck by an electrical spark. Later, while testing how lightning affected prepared frog legs, he saw them convulse when brass hooks in the frog's spinal cord touched the iron railing they hung from. He concluded that the frog itself held "animal electricity", the power that animated living things.

His contemporary Alessandro Volta did not buy it. Volta believed the twitching depended on the metal used to connect the nerves and muscles. In his reading, the frog's leg was just a wet conductor and a sensitive detector, while the real source of the electricity was two different metals touching.

To prove it, Volta built something remarkable. By 1800 he had stacked pairs of copper and zinc discs separated by brine-soaked cloth or cardboard, with no frog anywhere. It gave off a continuous current, the first true battery. The two men disagreed respectfully, and Volta even named the chemical production of current "galvanism", after Galvani.

So who won? Volta gave the world the battery. But Galvani was onto something real as well: every cell has an electrical potential, and living nerves do use electricity. The frog's leg was a real, sensitive detector of electricity, which is why it twitched.