They live by feeding on the blood of humans and other warm-blooded animals.
It would seem that there are two types of warm-blooded animal.
It would soon become the greatest mass destruction of warm-blooded animals in human history.
The lesson: In the far north, if you want to be up and about with the warm-blooded animals, you've got to dress like them.
But whether they were warm-blooded animals or reptiles, he could not decide.
All those characteristics I just listed are limited to warm-blooded animals in modern times.
He also did some of the early research into bioelectricity in warm-blooded animals.
For warm-blooded animals, a lot of energy is burned just keeping our body temperature where we need it.
"And they've gotten pretty good at finding warm-blooded animals like us."
No warm-blooded animal on earth uses more energy, for its size.