HP/Mana restore from killing Large Monsters

I've noticed when I kill a Large Monster or the Scuttlecrab when I am jungling, I get my HP and mana restored by a small amount. This occurs even when I do not level up from the exp gained. At first I thought it was a strange interaction with Dangerous Game (Mastery) where it procced off of monster kills as well, but I find that I get the HP and mana restore even when I do not have the mastery selected. Can anyone clear this up? Thanks.