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Snape And Dumbledore Hid A Fart Machine In Harry Potter's Sleeping Bag

Expelliarmus!

We thought we'd heard every amazing story to come out of the making of the "Harry Potter" movies, but apparently, delightfully, we were wrong.

Alan Rickman has been sitting on an absolute gem of an anecdote from "Harry Potter and the Prisoner of Azkaban," which he (ahem) let slip last night (June 17) on "The Tonight Show."

You might think you have some idea how this story will go based on the headline -- and yes, it is a story about how Rickman and Michael Gambon (Dumbledore) pranked Daniel Radcliffe with a fart machine -- but in reality, as told by Rickman, it's so much better than you can possibly imagine. Take it away, Professor Snape.