Fact 1: Mammals generate heat mainly by keeping their metabolic rate high.

Fact 2: Faster metabolism means more calories consumed, and usually, weight loss.

Given the two facts above, answer the question "How do mammals generate heat?" with the following options: 
- freezing
 - Ice cubes
 - layers of fat
 - Taking pictures
 - with their fur
 - energy of moving objects
 - Consuming calories
 - Movement of an air mass


 

       Consuming calories  