Fact 1: Mammals can also generate little bursts of heat by shivering.

Fact 2: Basically, heat is energy.

Given the two facts above, answer the question "What can a mammal produce by shivering?" with the following options: 
- energy
 - motion
 - food
 - warmth
 - cells
 - fur
 - light
 - matter


 

 energy        