Why does Rin in blue exorcist have an eye bigger than the other when uncontrollable? Why does Rin in blue exorcist have an eye bigger than the other when uncontrollable?

It also happens in Naruto, when he doesn't want to use his powers to fight Amaru when Amaru is possessed for example.
because his evil side is taking over and besides in every anime when their mad one of their eyes get smaller than the other