Which part of Luigi Galvani’s animal-electricity theory was incorrect?

Luigi Galvani’s theory of "animal electricity" was partially incorrect. While he correctly identified that electrical stimuli cause muscular contractions, he was mistaken in his belief that this electricity was an innate, vital force generated by the animal's own tissues, which he likened to a Leyden jar.1

His contemporary, Alessandro Volta, argued that the electricity was actually produced by the contact of dissimilar metals used in Galvani's experiments. In retrospect, both scientists were partially correct: Galvani was right that electrical forces exist within living tissue—a fact he later demonstrated by inducing contraction without the use of metal—but he was wrong to attribute the initial experimental results solely to an internal "animal electric fluid." Conversely, Volta was correct to reject the idea of an inherent animal fluid as the source of the observed current in those specific experiments, but he was wrong to imply that all electrophysiological effects require two different metals.1