It's scar tissue from where it was trying to get a shed off and rubbed the top of his head raw. I sold two ball pythons to someone local that decided to take the cheap way out on housing, and had them in a tub bungee corded on lid with a heat pad with no way to regulate the temp. Tubs got over heated and the humidity dropped down low, both snakes had the same scaring after a couple of sheds. Both snakes have been turned over to a new responsible owner, and are doing good. They have complete sheds and none gets stuck around the scar tissue.