National Kazoo Day takes place on January 28, 2019. The kazoo is a musical instrument that adds a "buzzing" timbral quality to a player's voice when the player vocalizes into it. The kazoo is a type of mirliton, which is a membranophone, one of a class of instruments which modifies its player's voice by way of a vibrating membrane.
A kazoo player hums, rather than blows, into the instrument. The oscillating air pressure of the hum makes the kazoo's membrane vibrate. The resulting sound varies in pitch and loudness with the player's humming. Players can produce different sounds by singing specific syllables such as doo, who, "rrrrr" or "brrrr" into the kazoo. (With material from: Wikipedia)