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This movie is based on Arthur Conan Doyle's Sherlock Holmes detective. Holmes (Nicol Williamson) has gone nearly insane because he is addicted to cocaine which he injects in a solution of seven-per-cent cocaine and water. Watson (Robert Duvall) tricks Holmes into going to Vienna where Dr. Sigmond Freud (Alan Arkin) attempts to cure his addiction using hypnotism. During his withdrawals from the drug, Holmes wakes one night after having a bad dream that a snake is in his room, which he calls "a swamp adder, the deadliest snake in India." We don't see the snake. After he calms down he tells Freud that he dreamt about a case he once solved in which a snake was sent down a bell rope above the bed of a woman to kill her as she slept (which is in the story called "The Speckled Band.") After Freud leaves, Holmes has more hallucinations of snakes. This time we see them - a bunch of snakes in his bed and a snake coming down a bell rope above his bed that stares into his face. Nothing else happens with the snakes, they are only hallucinations. The snakes we see are all harmless. The one on the bell rope is a Kingsnake. The snakes in the bed appear to be grass snakes (Natrix.)