Quick! Escape the lack of details by
clicking to enlarge this picture !
Like Brides of the Mansion, this strip requires some insight about the “real” Haunted Mansion to get where the meat of the gag lies (even though the expressions are good): the character of Gus the Prisoner appears two times (first in the "Executioner" tableau, and then in the "Hitchhiking Ghosts" tableau), ten second appart. This gag is trying to imagine why Gus leaves the first tableau so fast to join the second one.
A very interesting characteristic of this strip is that it is entirely mute, which suits Kelly's expressive style very well (you can easily get Gus's reasoning without any dialogue).
However, I do have a complaint about this gag, well-executed (*chuckle*) though it may be: it is unlikely that the Executioner was really planning to behead Gus, nor is it likely that the Beheaded Knight just got beheaded; the three of them are supposed to have been ghosts since a long time, and beheading seems to have been why the Beheaded Knight died in the first place. Of course you could interpret it as Gus being uselessly paranoiac, but it's not all that obvious.
Still, this strip is an enjoyable read. Also, rejoice: this was the last black-and-white strip, after that we switch to color permanently.