Contrary to legend, wild predators are actually incapable of smelling fear. However, their fleas are highly attuned to it... and they let their host know, whispering like the tiny flesh-eating demons that they are. This is actually why flea colonies tend to gather near an animal's ears. It's the easiest way to be heard.
As a matter of fact, 98% of all reported cases of demonic possession have been attributed to a simple case of having a rampant flea infestation.