Three post turtles.

What's a "Post Turtle?"

Excerpt from the joke:

The old rancher said, "When you're driving down a country road you come across a fence post with a turtle balanced on top, that's a 'post turtle'."

The old rancher saw the puzzled look on the doctor's face so he continued to explain.

"You know they didn't get up there by themselves, they don't belong up there, they don't know what to do while they're up there, and you just wonder what kind of dummy put them up there to begin with."