facial rubbing?

[pythonregius]

for some reason my ball python has begun to rub his face into the glass of his tank. he does this quite often now and it looks like he is doing it quite hard to for everytime he gets near his eyes, he presses hard enough so they "sink" into his head ever so slightly. but they always return to their "normal" state. i have not owned a ball python for long, i actually came into ownership of this one due to its poor living conditions from its previous owner. i coul't stant to watch it like it was so i took it. i have never really liked snakes but for some reason this ball python is begining to grow on me over the months. and i actually don't mind the husbandry aspect of it either.