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

Fact 2: An inability to shiver or react to the cold can contribute to hypothermia.

Given the two facts above, answer the question "Mammals can also generate little bursts of heat by what?" with the following options: 
- the body's largest organ
 - reacting to the cold
 - flow of electrons
 - looking very cold
 - reacting to the news
 - considering being warm
 - Movement of an air mass
 - with their fur


 

  reacting to the cold       