Derek raised an eyebrow, and reached for a rag, wiping the boy's hands clean as he considered the best way to respond. He sat back down, and drew Stiles into his lap, brushing his lips against the boy's shoulder and neck. "There are certain behaviors...some things that mean something different to a werewolf than to a human," he began, slowly. "Pack behaviors. When you bit my neck, I reacted like a wolf would to a challenge."