There's a whole scene where they mutiny against their leader because they're starving and dog tired. They want to eat the hobbits, and the only thing that stopped them was one of them getting beheaded for mutiny, and then getting decimated by a squadron of Rohan horsemen. I love that they took the time to include that, since it makes it more believable. The Uruk-hai were pushed to their absolute limits and then beyond, and they snapped, just like men would.