My son who is soon to be 4 years old is biting himself typically all up his arms. He is doing this hard enough that he leaves marks. When I ask him why he is doing this he said it will make me happy. I tell him that it doesnt make me happy it makes me sad that he is hurting himself he will reply with it doesn't hurt it feels good. I am not sure what I should do to make this behaviour stop. Is this a sign that there may be something wrong with my son??