Every novel uses literary devices to some extent, and Paul Zindel's The Pigman is no exception. I have included a link to the eNotes Guide to Literary Terms so you can see the wide range of possible literary devices (terms) one might find in a short story, novel, or poem; many of them will undoubtedly be familiar to you and you will be able to find examples of them on your own. Hyperbole and understatement, for example, are two which are common and easy to find in this text. I have selected a metaphor and a symbol as two more complex examples of literary devices used in the novel.
Lorraine sees a little statue of "three little monkeys in a cage that were hugging each other like crazy," and immediately she sees this as a symbol of the rather odd little friendship she, John, and Mr. Pignati share. She makes the connection herself:
We must have looked just like three monkeys. The Pigman, John, and me—three funny little monkeys.
One consistent metaphor (comparison) which permeates the novel is being in a cage. Of course the monkeys in the zoo are in real (literal) cages; however, many of the human characters in The Pigman are also in figurative cages of some kind. Lorraine feels trapped (caged) by her mother's constant suspicions, and her mother is stuck (caged) in a terrible job. John feels trapped by his father's assumptions about his future career, and John's father is confined by his small world, the Coffee Exchange. Mr. Pignati, of course, is immobilized (caged) by his grief over the loss of his wife.
At the bat exhibit one day, Lorraine has this experience.
[A] little kid about ten years old who was sitting right up on the railing and leaning against the glass of the bat cage. Only he wasn't looking at the bats. He was looking at you when you came to look at the bats. And when I came up to the cage to see these ugly blood-sucking creatures, I had to look right into this little kid's face that had a smirk on it. He made me feel as though I was a bat in a cage and he was on the outside looking in at me. It all made me very nervous.
Though she uses simile here (using like or as to make a comparison), the imagery of the cage metaphor begins early in the novel and continues throughout.
These are two good examples of metaphor and symbol, as well as a simile. Literary devices can literally be found everywhere in fiction; the difficult part sometimes is knowing (or remembering) what they are in order to find some examples.