What the Nintendo nunchuk looks like.

The nunchuck is the controller that comes with the wii and is used for 3d navigation games (most of the time), such as Super Mario Galaxy. The nunchuk has 3 buttons and a cable to plug into your wii remote, the three buttons are: joystick, Z button and the c button. The nunchuk happens to have sensors integrated inside the controller. The main use of a nunchuck is to play Mario Kart: Double Dash!! on a wii without having to use a Nintendo GameCube (controller).

External links

An article on the wii nunchuk: [1]