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It was because of a war wound that cost Canadian actor James Doohan the finger on his right hand. But he never let the audience see the digit was missing.
The things you learn all these years later.
Star Trek icon's horrific WW2 injury – and how he hid it on sci-fi set
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Gary Burghoff on M*A*S*H did the same with his left hand. It's rarely visible on screen but you can catch the odd glimpse.
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Game show host extraordinaire Bill Cullen had polio as a kid and walked with a very pronounced limp. You never saw it on TV, because they always introduced him already sitting in a chair, so no one knew. He never walked onto the set like all other game show hosts did.
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