Keith Richards has answered another question on the Ask Keith section of his website. Asked "What's something you've only tried once," he says, "Elephant tranquilizer... I tried it once and God help the elephants."
Another Keith, Keith Moon, also reportedly had a bad experience with an animal tranquilizer, just before going onstage for the first night of The Who's Quadrophenia tour on November 20th, 1973 in San Francisco. He passed out on stage, forcing Pete Townshend to recruit an audience member, Scott Halpin, to play drums for the rest of the show.

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