Let's follow a fly through a frog's body and find out!
Mouth: When the fly is captured by the frog, a patch of small teeth in the frog's mouth prevent it from escaping the way it came through. The frog swallows by pushing the fly down toward its esophagus with its eyeballs. That's why a frog blinks every time it swallows.
Esophagus: Ciliated cells push the fly down the frog's esophagus.
Stomach: Here's where the work starts. The fly is dropped into the frog's stomach, and here it is acted upon by digestive enzymes. The fly is stored in the stomach until the soft parts of its body are liquefied. Since frogs have no ribs, just by feeling a frog you can tell if its stomach contains any insects!
Small intestine: What's left of the fly goes here. It is completely digested in the small intestine, and from there nutrients are absorbed from it.
Large intestine: The parts of the fly which are unusable go here and leave the body as waste.