I can’t think of a single non-Arlo interpretation…
This is one reason you empty out the pumpkin before carving it.
But what’s the joke here?
B.A.: Is the joke the fact that Janis used the word “mob,” which normally would be something the Monster wouldn’t welcome?
This kind of thing might be rare, but does it really cross over to “mean”? When my kids were young — probably the ages of the kids here — I was taking them around on Halloween and the scarecrow on one of the porches (actually the homeowner in disguise) came to life and shouted “Boo!” as the kids rang the doorbell.
(And this was a whole lot more startling that somebody already dressed as a skeleton removing his fake head)
But once regular heartbeats resumed, everybody thought it was awesome.
A commenter at the GoComics site wrote “there’d be more than one parent calling the police.”