Well, it's got the lady's odd predicament of swallowing that fly. Then there's her attempts to solve the problem by swallowing other things like a spider, a bird, and so on. The escalating sequence of events is a key part of the story.
The key elements are the lady's unexpected act of swallowing the fly, her growing desperation as she keeps swallowing more to fix the situation, and the humorous and sometimes absurd chain of events that follows.