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1.
The product of inbreeding, A.K.A. incest, or doing your family members, results in messed-up little creepers. Or messed up big creepers. Or something somewhere inbetween.

These people tend to have physical abnormalities and mental issues (in other words, they are totally screwed over in life). They go screwy in the head and tend to act wacky. It fits their appearance.
These are all examples of a product of inbreeding:
Mordred, the son of Arthur and his sister

Hillbilly children, the result of bored country hicks

Your mom- lol