Kazoo

Simple but funny and nice instrument. And really simple for playing.

Some information from Wikipedia:

The kazoo is a wind instrument which adds a "buzzing" timbral quality to a player's voice when one vocalizes into it. The kazoo is a type of mirliton which is a membranophone – a device which modifies the sound of a person's voice by way of a vibrating membrane.

While blowing is the term typically used to describe the technique required to play a kazoo, a more accurate term would be humming into the kazoo. Blowing with the lips closed around the mouthpiece of the kazoo will not make sound – one must vibrate air from his or her lungs by humming into the instrument in order for the kazoo to make any sound. Increased air flow and harder blowing will result in a more effective and authoritative sound.