Smelling fear

It sounds crazy but you can actually smell fear.  Fear induced odors trigger improvement on certain tasks.  Certain odors can cause a heightened sense of cautiousness, which will make you act more carefully while doing certain tasks.  Smelling fear is very common in animals due to the fact that some animals are dangerous and other animals can sense that. https://www.youtube.com/watch?v=zmksQTVs_vU