Two U.S. researchers say most theories of humor come up short in one way or another, but they say immoral behavior is funny only if it is harmless.

A. Peter McGraw of the University of Colorado-Boulder and co-author Caleb Warren say humor comes from seeing violations or threats to the way the world ought to be that are harmless.

McGraw -- referring to Three Stooges slapstick -- explains Moe hitting Larry is funny because Larry's not really being hurt.

"It's a violation of social norms. You don't hit people, especially a friend. But it's OK because it's not real," McGraw said in a statement.

The study, published in Psychological Science, confirmed people who have more psychological distance from a moral violation were more likely to be amused. For instance, study participants were asked to read a scenario where a church or a credit union raffles off a sport utility vehicle to attract new members.

Study participants said they were disgusted when the church attracted members with a car raffle, but not the credit union. But whether they were amused by the church depended, in part, on whether they went to church or not -- non-churchgoers were more likely to think that was funny. (c) UPI