In the way they walk?

I thought this was interesting-they studied the way people walk and had observers guess if the walker was gay or straight based on how they look walking. People were accurate with gay males 60% of the time (but with lesbians they couldn't tell).
“There’s reason to think that gay people can’t conceal their homosexuality,” says Michael Bailey, a professor of psychology at Northwestern University. “I don’t think it’s a performance that gay people enact. I think it’s something that either is inborn, or it’s acquired very early, perhaps by watching members of the other sex.”