A group of tourists spot a cowboy lying by the side of the road with his ear to the ground.
"What's going on?" they ask.
"Two horses - one grey, one chestnut - are pulling a wagon carrying two men," the cowboy says. "One man's shirt is red, the other's black. They're heading east."
"Wow!" says one of the tourists. "You can tell all that just by listening to the ground?"
"No," replies the cowboy. "They just ran over me."