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

Fact 2: Shivering heats the body.

Given the two facts above, answer the question "what does muscles contracting a little bit all at once do?" with the following options: 
- biceps
 - cause death
 - respiration
 - staying warm
 - rapid expansion
 - movement
 - heat the body
 - to move people


 

       heat the body  