Timber does that too. I used to give her treats often, but now that she's at my aunt's she rarely gets them, and so she gets very excited and just goes for the hand. It's very painful. I often make her sit and then say in a calm soft, but warning voice "Niiice..." and very slowly and gently give it to her while holding the scruff of her neck so that she knows I'm in control, I'm boss, and I this is her gift, not her right.