In 1929, researchers at Princeton University claimed that they had turned a living cat into a telephone.
In 1929, Princeton professor Ernest Glen Wever and his research assistant Charles William Bray set out to learn more about how sound is perceived by the auditory nerve. To do so, they needed access to a real auditory nerve. Enter a sedated, but still very much alive cat.
First, they opened the cat's skull, to gain access to its auditory nerves. Then, they attached one end of a telephone wire to the nerve, and the other to a telephone receiver, effectively creating a transmitter. Wever then took the receiver and went into a soundproof room 50 feet away. To their surprise, when Bray spoke into the cat's ears, Wever could hear him through the receiver.
The results of their experiment turned out to be larger than they imagined. The common theory at the time was that when a sound got louder, the frequency would get higher. Wever and Bray's experiment provided proof of that theory.
The discovery of the frequency correlation led to other medical breakthroughs and even helped the military during World War II.