When you are hungry, your stomach growls. I have a theory that, long ago, all our body parts growled for attention. For example, if you leg itched, it would start growling. That is how you would know to scratch it. But, when we invented movie theaters, it became difficult to hear the movie because of all the growling, so humans evolved to have our body parts not growl anymore. But, our stomach was too stubborn to evolve, so it still growls.
I didn't say it was a good theory.