Revealing mistake: When Gary and Wyatt come home and see Chet turned into a pile of poo, Chet shoots his tongue from his mouth and catches a fly. Look closely, the tongue flies completely out of his mouth and is attached to a metal spring. (01:24:55)
Revealing mistake: Arriving home from his hunting trip, Chet Donelly (Bill Paxton) finds Gary in bed with a girl. Chet whacks them both over the head with his rifle and you can clearly see the barrel bend with each hit. (01:13:54)
Revealing mistake: There is a visible cord pulling the couch during the scene where furniture is sucked out the chimney. (00:55:50)
Revealing mistake: Wyatt's grandmother is supposed to be frozen solid, however she moves a bit when we see them in the closet.
Revealing mistake: When Gary is being chased by the police, a stunt double in a blond wig is driving his car. (01:20:35)
Answer: According to the Wikipedia page for this movie, Lisa transforms Chet into a giant, talking turd.
Casual Person