I picked up a couple of barred rocks at the feed store today. One was marked like a male. I told them I didn't want that one because it was a boy. The girl who works there picked it up, looked at its butt and said, "Nope, it's a girl." Then she picked up another and did the same thing. She didn't check the vent, just turned the chick over and looked at the butt. Isn't she clever to figure out chick sexing that way?