Today one of my silkie chicks was squeaking loudly. All 4 have been fine up to this point. They are in a brooder on paper towels with medicated chick feed & water. After watching for a while, the chick will suddenly open his beak very wide, drop his head down and his body will shake like chickens do after a dust bath, as if shaking out the dirt from feathers. He squeaks loudly, then will close his eyes & lay down until the next one. He is pooping normally. Any ideas what this could be?