The three omens that Lorraine thinks she sees at the zoo are the lady selling peanuts, the peacock, and the kid sitting outside the vampire bat exhibit. She thinks the omens are saying that bad things are going to happen as a result of their involvement with the Pigman.
The first omen is a woman selling peanuts. Lorraine goes up to her and asks for four bags. The lady is very rude and antagonistic - Lorraine says, "You could tell she hated kids - just hated them." To Lorraine, that is the first omen, and she wishes she and John had "left right on the spot."
The second omen is when she is "attacked" by a peacock. A large white peacock opens up its feathers and starts dancing in front of her when she opens her first bag of peanuts. Frightened, Lorraine backs up against a fence, and she is not reassured when the Pigman just grins and tells her, "Just offer it a peanut...He likes you. Ha, ha."
The third omen occurs in the nocturnal room of the Mammal Building. Lorraine "almost (goes) into shock" when she gets a good look at the vampire bats, who are shown with accompanying pictures of a couple of them "sucking the blood out of a horse's neck." The creepiest part about the exhibit, for Lorraine, however, the part that she considers to be an omen, is a child that is sitting in front of the bat cage. The little boy isn't looking at the bats; he is "looking at you when you (come) to look at the bats," smirking. The kid makes Lorraine feel uneasy, as if she is a bat in the cage and he is on the outside looking at her (Chapter 6).