Hmmm.... That's very odd indeed. I think I missed a number in there somewhere.... I'll add it to my list of fixes. What do you mean a skull? Like a status condition?
Ah. That's the Overstuffed state. So basically, if you exceed your maximum fullness (press 2 on the keyboard to get an exact number), you receive a debuff. Seems like it's not disappearing when you drop below the threshold though which is annoying...