Often, something is seriously funny. The world's best joke, for example, as researched by psychologist Dr Richard Wiseman:
Two hunters are out in the woods when one of them collapses. He doesn't seem to be breathing and his eyes are glazed. The other guy whips out his phone and calls the emergency services. He gasps: "My friend is dead! What can I do?" The operator says: "Calm down, I can help. First, let's make sure he's dead." There is a silence, then a shot is heard. Back on the phone, the guy says: "OK, now what?"
I also like the European favorite a lot:
An Alsatian went to a telegram office, took out a blank form and wrote: "Woof. Woof. Woof. Woof. Woof. Woof. Woof. Woof. Woof." The clerk examined the paper and politely told the dog: "There are only nine words here. You could send another Woof for the same price." "But," the dog replied, "that would make no sense at all."