It is a piece of aluminum that when the tailgate is down, it covers the gap between the bed of the truck and the tailgate.  When cleaning out the bed of the truck, small debris doesn't fall into the gap, which usually ends up on the bumper or the on the ground.  When the tailgate goes up, the foxtail slides up out of the way.
postal j 08/02/2014
Great idea Randy! I have the same idea. Instead of aluminum, I believe that a flexable material work such as plastic would work as well a metal.