Like many famous musicians, shock rocker Alice Cooper doesn't feel right about going onstage till he finishes a special pre-show ritual.

"I throw knives," he told Dave Grohl, who dressed up as David Letterman while filling for Jimmy Kimmel on Halloween. "I pick out people and I put them on my board. And I throw knives [at them]."

Those targets include Kimmel's arch-nemesis Matt Damon, whose face was used for a demonstration on the show.

And Cooper isn't the only frontman with a weird pre-show routine.

"Every lead singer I know has some sort of idiosyncrasy ," he added. "Roger Daltrey fly fishes in his room, he practices. Peter Frampton irons. We used to throw all of our clothes into his dressing room."

Alice also told Grohl about the time he spent a night with Aerosmith's Joe Perry in a haunted house. Check out the story in the clip above.