The umbreon is in his hunting season and that usually matches up with his heat timing, if a prey can catch him off guard he will get sensitive and will let then go. The prey has two options then, run away or take advantage or his defenseless big knot in their face. Most run but others will play with it and suck it as a thank you for being a easy predator to escape since his heat disrupts his hunting, it works sometimes not always. (Pokemon can't talk so they communicate through faces and sounds)