And if they don't appear to have a deformity at first, they'll be disguised and pull it off at the last minute. Heck, I even used that cliche in a story. The bad guy had been mutated in an accident and he wore sunglasses to hide the fact that he had eyes like a snake.

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"If you think the LHC will create black holes, you might as well believe Hobbits are at the bottom of your garden."- Dr. Mike Inglis
Rovers forever! - ToSeek
"Carl Sagan sent a message to ET,
Neil Armstrong walked in the Sea of Tranquility
Steve Squyers built Spirit and Opportunity
Dan Haylen upchucked in zero gravity." -Brent Simon, The Space Camp Song