From Logan (aka Logan Tygart) [sltygar@adelphia.net], this was published on alt.humor.puns and the groaners listserv.

Once, while driving around in my pickup with my pet donkey in the back, I discovered I had a flat tire. I got out and had the donkey stick its head under the bumper and lift the truck.

A passing farmer asked, “Hey, that’s a pretty clever trick. How did you teach your donkey to lift the truck?”

I replied, “Its a simple matter of the breed; this is a jack ass!”