hungertale is an au where a zombie apocalypse started on the surface and spread to the underground Sans was infected and received a crack on his skull and lost his left arm. he eats infected and sometimes normal souls to survive, he tries to not hurt any soul for Papyrus. He can only see people with a soul but he can still but he can still see their clothes and bump into them. Papyrus is still mostly the same besides the fact he became a scientist to try and find a cure for the infection