Yeah, a huge patch of heat barely visible behind a tree.

Scanning your head back and forth slowly over the forest behind you, you narrow your eyes at some of the more suspicious looking plantlife, before focussing in on one particularly strange looking tree. To a normal humans eyes, it would have been completely indistinguishable, but with your sharpened thermal vision you can make out a subtle difference, two different signatures that very nearly blend together into one. You can't quite tell what it is, until it makes the tiniest motion possible. A breath.

Something's following me.