It hurts. Eventually, everyone encounters hurt. Life is one big pain if you let it become one. It physically hurts like nothing he's ever experienced when August begins to turn into wood again. And it mentally, emotionally hurts in an entirely different way when the transformation is complete, and he realizes what sort of a freak he's become.
It hurts. It hurts like nothing else that Snow has ever encountered when Regina shows her that her heart is blackening. There's nothing she can do to stop it, and that terrifies her.
Then she finds August, and they help each other.