His insistence on "animal electricity" and not metallic or atmospheric electricity was that while he could certainly make the frog legs jump when in contact with 2 metals and also during thunderstorms, there were times when the frog legs contracted on perfectly clear days without a complete arc of two metals. This stirred up quite a controversy with Galvani on one side and Allesandro Volta on the other in support of metalic electricity.
Animal electricity was rejected after Volta succeeded in making the first battery with 2 different metals (no animal involved). It was not until the 1830s that Carlo Matteucci's experiments establish the existence of animal electricity in injured muscle.
Fun Word Facts: Galvanized, galvanism, and galvanometer are all derived from Galvani.