The existing drawings, based on historical descriptions of the Katzenklavier, suggested that the instrument consisted of a keyboard, with seven to nine cats held in cages corresponding to the approximate pitch of their mewling.

Each of the cats’ tails is stretched out and held down. Above each tail is a nail. Depressing a key assigned to a specific cat causes a mechanism to drive the nail into the tail resulting in a shriek from the poor animal.

It was invented sometime in the 17th century by Athanasius Kircher, a German Jesuit renaissance man operating in the fields of medicine, oriental studies and geology.

[T]he device was intended to shake mental patients who had lost the ability to focus out of a “fixed state” and into “conscious awareness”. The patient must be placed so that they are sitting in direct view of the cats’ expressions when the psychiatrist plays a fugue on the infernal instrument.

Via The Guardian.