Why did Luigi Galvani believe electricity caused muscle fibers to contract?

Luigi Galvani believed that muscle fibers contracted because they were stimulated by an innate, vital force he termed "animal electricity."1

Through his experiments, particularly with frogs, Galvani concluded that this electric fluid was secreted by the brain and conducted through the nerves to the muscles. He theorized that the muscle and nerve tissues functioned similarly to the inner and outer surfaces of a Leyden jar, a device used to store static electricity. When these tissues were spanned by a conductive arc—such as metal probes—the resulting flow of this internal electric fluid provided the necessary stimulus to trigger the contraction of the muscle fibers.1

While he was correct that electrical stimuli cause muscular contractions, he was mistaken in his belief that this was a unique "animal" form of electricity, as the phenomenon is actually driven by electrochemical processes within living tissue.1