You are presented with the quiz "What occurs when many muscles contract a little bit all at once?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "shivering occurs when many muscles contract a little bit all at once" and "involuntary contractions, shivering, cause the production of heat". 

So, what's the best answer to the question?


 

    the production of heat       