According to Charlie Day and Glenn Howerton, the scene where Dennis and Mac helpĀ Charlie make his dating profile was scripted but “loose,” leaving Day open to riff on the scripted elements to try and make his co-stars laugh. The idea for ghouls, however, came from Howerton, who explained their origins:
“Now, where that came from was when I was a kid, we had this book, this Halloween book and I think it was called, ‘It’s Halloween.’ And it was a book of, like, little Halloween poems and all these, like, little Halloween stories. And I just remember this one story, like really standing out to me where there was like a ghoul sitting on a tree outside of this kids window. And the kid didn’t know why the ghoul was there. And just thinking that that was a funny, I don’t know why, but I don’t know why, but I remember it striking me that that would be a funny thing for Charlie to like. There’s something funny about just, like, it’s not a ghost. It’s not a ghost.”
This leads the guys to discuss the differences between goblins, ghosts, and ghouls, revealing that the main difference is that there’s a light-hearted nature to a ghoul that isn’t there in the other two. In fact, Howerton and Day really have a lot of opinions about ghouls and goblins.