What to do

Caleb has started pulling hair and biting. So I think that I am going to get my hair cut to help my hurting head, but I'm not sure what to do about the biting. Now that he has 5 teeth (2 on the top and 3 on the bottom) it really hurts if he bites. He mostly does shoulder biting but he will get you other places too if you give him the chance. I also don't know how much he understands the concepts of "no" and "don't do that" since he usually just smiles or laughs when I tell him to stop. Maybe I don't have a mean enough look on my face when I say it. So all of you psychology people, at what age do babies understand the concept of "no" and how do you get them to stop. And I have pulled what little hair I could and bit him, not hard but so he could feel it, but he is still doing it so I need another idea.

Caleb is using his walking toy more these days and so he might be walking soon. I don't think he will be near Eli's level real soon but I guess we will have to wait and see. It was weird to see Eli walking so well when we saw them. I heard that he was walking but wow that was impressive.