Thanks, all. Now it makes sense.
Here's info from Wikipedia:
The Nunchuk (model number RVL-004) is the first controller attachment Nintendo revealed for the Wii Remote at the 2005 Tokyo Game Show. It connects to the Wii Remote via a cord that is about 3.5 to 4 feet (1 ~ 1.2 m) long. Its appearance when attached resembles the nunchaku, hence the name. It also features an analog stick similar to the one found on the Nintendo GameCube controller and two trigger buttons (a last minute modification changed the two triggers to one trigger and a "C" button, as described below). It works in tandem with the main controller in many games. Like the Wii Remote, the Nunchuk also provides a three-axis accelerometer for motion-sensing and tilting, but without a speaker, a rumble function, or a pointer function. The Nunchuk's accelerometer is an STMicroelectronics LIS3L02AL.