A cowboy is pulled over by a cop.
The cop lectures the cowboy about speeding.
Finally he gets around to writing out the ticket. Flies begin buzzing around his head.
"Problems with circle flies?" asks the cowboy.
"If that's what they're called," says the cop. "I never heard of circle flies."
"Circle flies hang around ranches," says the cowboy. "They're called circle flies because they usually circle the rear of a horse."
"Oh," says the cop. Then he stops. "You calling me a horse's ass?"
"Oh no, sir," the cowboy replies. "I respect law enforcement too much to call you a horse's ass."
"Good thing," mutters the cop, finishing off the speeding ticket.
After a pause, the cowboy says in his best drawl, "Hard to fool them flies though."