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When Harry first meets Professor Quirrell in the bar with Hagrid, Harry extends his hand to him to shake it, but Quirrell makes it a point not to shake it. It is shown at the end of the movie that when Harry does touch Quirrell, it causes him to physically break down due to his dark magic and association with Voldemort. It is later revealed in Harry Potter and the Goblet of Fire (2005) that unless he finds a way around, Voldemort cannot touch Harry due to a magical incantation that occurred when he tried to kill Harry as an infant.
Alan Rickman was handpicked to play Snape by J.K. Rowling, and received special instructions from her about the character. Rowling even provided him with vital details of Snape's backstory, not revealed until the final novel.
The child actors and actresses would do their actual schoolwork in the movie, to make the school setting more real.
Richard Harris, who had been acting for more than forty years by the time this movie entered production, stated that he had never been involved with a cast that was as close as this one.
Richard Harris had trouble remembering his lines, and Daniel Radcliffe would ask him to help with running his lines, just to give Harris more practice.
The Hogwarts' motto, "Draco dormiens nunquam titillandus", means "never tickle a sleeping dragon".