These guys walk really slowly but can run at a top speed of 90mph. A group of them is called a "Sulking" as they look like they're constantly crying. The skull is not a real skull, it's just an armor plate. It can lie on the ground and pretend to be a corpse to avoid predators. Occasionally, scavengers do get a peck/nip or 2 at them before getting shaken off by the creature.