Have you heard the one about the eager experimenter who swallowed a balloon? The results burst his ... well, hypothesis.
One daring researcher, as part of an early investigation into the causes of hunger, fasted before downing a deflated balloon attached to an air tube. Upon reaching his stomach the balloon was inflated. Recordings of pressure changes in our poor PhD's gut proved that the stomach contracts when empty. It is these muscle contractions that cause those pre-lunch pangs, and it was long thought that they caused our cravings for food as well.
But further research proved that cravings persist not just sans contractions, but in the absence of a stomach as well! (Don't ask about the sad sap who proved that one.)
As it turns out, hunger speaks not from the belly but from the brain (the growling of our stomachs is actually the movement of digestive gases and juices in the small intestine). The hypothalamus in the brainstem largely regulates eating behavior. So you might wonder about the hypothalamus of a person who'll chow down on balloons, even in the name of science.