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

Fact 2: Another response to cold is shivering.

Given the two facts above, answer the question "A response to what occurs when many muscles contract a little at once?" with the following options: 
- heat
 - cold
 - sweat
 - pain
 - forces
 - stress
 - comfort
 - motion


 

  cold       