Why was the Jack O’Lantern scared?

The joke “Why was the Jack O’Lantern scared? Because it didn’t have guts!” is a play on words that combines the traditional activity of carving pumpkins for Halloween with the concept of “having guts.” In common parlance, “having guts” is an idiom that means having courage or bravery. When someone is said to “have guts,” it means they are fearless or bold.
In the context of the joke, the term “guts” is used literally to refer to the insides of a pumpkin. When carving a pumpkin to make a Jack O’Lantern, the first step is usually to scoop out and remove the seeds and pulpy insides, which are often referred to as the pumpkin’s “guts.” The joke humorously suggests that the Jack O’Lantern is scared because it has had its guts removed, playing on the dual meaning of the word “guts” as both the literal insides of the pumpkin and the figurative concept of courage.