A cat piano or Katzenklavier (German) is a hypothetical musical instrument consisting of a line of cats fixed in place with their tails stretched out underneath a keyboard. Nails would be placed under the keys, causing the cats to cry out in pain when a key was pressed. The cats would be arranged according to the natural tone of their voices.

The instrument was described by German physician Johann Christian Reil (1759-1813) for the purpose of treating patients who had lost the ability to focus their attention. Reil believed that if they were forced to see and listen to this instrument, it would inevitably capture their attention and they would be cured (Richards, 1998).