Clone machines make copies of monsters and blocks when their controlling button is pressed. It is worth distinguishing between the behavior of `wired' clone machines and `normal clone machines'.
A `normal' clone machine is controlled by the red button tile. Red buttons are linked to clone machines in reading order. If there are two red buttons in reverse reading order of the clone machine, both will be linked to the same clone machine. If the clone machine is blocked in the default direction when the button is pressed, no clone will be produced.
A `wired' clone machine is attached to an electricity circuit. Every time the circuit state is TRUE the machine attempts to produce a new clone in the default direction. If the default direction is blocked, the machine will try to produce clones in the other three directions (in clockwise preference). A wired clone machine attached to an inverter repeater circuit and unblocked in all four directions can produce new clones at the astonishing rate of 20 per second.