Fact 1: Shivering occurs when many muscles contract a little bit all at once.

Fact 2: Heat production is increased by shivering and non-shivering thermogenesis .

Given the two facts above, answer the question "what happens when many muscles contract a little bit all at once?" with the following options: 
- heat is produced
 - To keep their body heat.
 - biceps
 - sweating
 - digestion
 - rapid expansion
 - preventing heat transfer
 - death


 

 heat is produced        