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 "When many muscles contract a little bit, simultaenous, it produces:" with the following options: 
- forces
 - heat
 - cold blooded
 - sweat
 - electrical energy
 - Energy
 - pain
 - thermal displacement


 

  heat       