Useless machine

A "useless machine" is a simple device or contraption that serves no practical purpose other than to perform a single, often humorous action when activated. The most common form of the useless machine is a box with a toggle switch on top. When a user flips the switch to the "on" position, a mechanical arm inside the box emerges and promptly flips the switch back to the "off" position, effectively negating the user's action.