Super Mario Brother Teresa Boo Ghost Sensor Light
Boos (originally known as Boo Diddleys and later Boo Buddies) are common ghost-enemies in the Mario series that first appear in Super Mario Bros. 3. They are a type of white spherical ghost with menacing and constantly open mouths. They are known for their large tongues and small "arms" of some sort. However, the most distinctive characteristic of the Boos is their shy personality where they cover their faces when someone looks them directly at the face but will uncover their faces once the subject turned around. Goombario's tattle for the Boo Igor in Paper Mario states: "He probably was a merchant before he became a Boo," implying that current Boos may have once been living beings. It is revealed in Super Mario Galaxy that they speak in Booish.