I've never heard of an apparition appearing as a skeleton before.
Creepy, huh? I wonder if Bill knows more about the "other side" than he is letting on?
The camera's flash causes a reflection of the ripples in the poster onto a perpendicular, adjacent wall. Coincidentally, it looks similar to part of a skeleton, minus the arms, head, and anything else that would be vertical instead of horizontal like the ripples in the poster.
Or, maybe it's a dead rugby player. Who knows?