The Brazen Bull was a hollow brass statue crafted to resemble a real bull. Victims were placed inside, usually with their tongues cut out first. The door was shut, sealing them in. Fires would then be lit around the bull. As the victim succumbed to the searing heat inside, he would thrash about and scream in agony. The movements and sounds, muted by the bull's mass, made the apparatus appear alive, the sounds inside like those of a real bull. This effect created additional amusement for the audience, and served the added benefit of distancing them from the brutality of the torture, since they couldn't directly see the victim.
Legend has it that this device was invented by a Greek named Perillus (Perilaus in some sources) for a tyrant named Phalaris of Agrigentum. Expecting a handsome reward for his creativity, Perillus instead became the first person placed inside the Brazen Bull. By some reports, Phalaris himself became an eventual victim of the bull when his subjects grew tired of his mistreatment [source: Gallonio].