[He tries to struggle away for about two seconds, confused, concerned that maybe Merlin's injured and not letting it on, concerned that maybe it's his own blood and all that -- but pretty soon he can't think much at all as he's held down and he gets enough of Merlin's blood for the change to take over]
[He gasps out once and tenses up at the sudden pain of that transformation, made worse by the fact that he doesn't understand what's going on or what's happening, only that it hurts and he thinks he's dying]