I suspect Scott is right, Ghosts is probably funnier to him than everyone else. I also suspect there are many ways it could have been made funnier.
It's not that the joke isn't clear, it's just presented in such a milquetoast manner that a lot of the funny is sucked out of it.
A couple people have commented on Francis' expression in the last panel -- I'm pretty sure I understand what's going on:
The line across the eyes aren't eyelids, or at least they aren't his top eyelids. If you look closely you can spot very small pupils looking off stage right. The lines are Francis' bottom eyelids, pulled up as he makes a pinched-face "I'm frightened" look.