A cowboy gets pulled over by a State Trooper for speeding. The trooper started to lecture the cowboy about his speeding, and in general began to throw his weight around to try to make the cowboy feel uncomfortable.
Finally, the trooper got around to writing out the ticket. As he was doing that, he kept swatting at some flies that were buzzing around his head. The cowboy sez, "Y'all havin' some problem with circle flies?"

The trooper stopped writing the ticket and said, "Well yeah, if that's what they're called. But I never heard of no circle flies."

"Well, sir," the cowboy replies, "Circle flies hang around ranches. They're called circle flies because they're almost always found circling around the back end of a horse"

The trooper says, "Oh," and goes back to writing the ticket. But, a moment later he stops and says, "Are you callin' me a horse's ass?"

"No, sir," the cowboy replies. "I have too much respect for law enforcement to call y'all a horse's ass."

"That's a good thing," the trooper says and goes back to writing the ticket.

After a long pause, the cowboy, in his best Texas drawl says, "Hard to fool them flies though."