The Killer Rabbit of Caerbannog is a fictional beast from the movie Monty Python and the Holy Grail. According to Tim the Enchanter, it "[has] a vicious streak a mile wide!", as well as "nasty, big, pointy teeth!" The creature has become known as the vorpal bunny, although this name does not appear in the film.
The Cave of Caerbannog ("Caer bannog" being Welsh for "turreted castle") is the home of the Legendary Black Beast of Aaaaarrrrrggggghhhhh, and is ostensibly guarded by a fearsome predator of an unknown description, because no one who attempts to enter the Cave or face the monster has ever lived to tell the tale.
The beast appears to be a cute, fluffy white rabbit, surrounded by the bones of the fallen. Despite Tim's warnings, King Arthur orders one of his knights, Bors, to decapitate the rabbit. Bors approaches it, sword drawn, and is immediately decapitated by the rabbit to the sound of a can opener. The knights attack in force, but are driven into retreat as the rabbit leaps and attacks, killing Gawain and Ector.