The White BuffaloGoofs
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Wild Bill Hickok often wears dark glasses. While there is a factual basis to this characterization. (In 1876, Hickok was diagnosed by a doctor in Kansas City, Missouri, with glaucoma and "ophthalmia.") Sunglasses were not invented until 1929 by Sam Foster, founder of the Foster Grant company, whom sold the first pair of Foster Grant sunglasses on the Boardwalk in Atlantic City, NJ.
Crazy Horse only learns of Hickok's true identity when Charlie curses him at the end. However, earlier in the film, as Jack Kylene is challenging Hickok on the mountain, he shouts his name numerous times before Crazy Horse kills him with arrows. Kylene's voice echoes repeatedly. Crazy Horse would easily have heard him.