Fluffy

From Hpwiki

Fluffy is a giant, three-headed dog, and one of Hagrid's pets. Fluffy was used to guard the Sorcerer's Stone in Harry Potter and the Sorcerer's Stone.

Fluffy's weakness is music. Music will cause him to go to sleep enabling people to pass him safely (but only until the music stops).

Note: The mythical background for this dog is Cerberus (Kerberos, Zerberus) who, according to Greek mythology, guards the entrance to the Hades (Hell). Cerberus wags its tail at everybody coming in, but he will let no one out. Living travellers use cakes to calm him down.