Jack. Stares, for a long moment, mouth hanging open. Then a faint flush creeps over his cheeks and he blinks a bit, before moving forward, towards the dangerous-looking creature Spike has turned into.
He's Jack. Even before he was made immortal, he had no real concept of personal danger.
His hand is reaching out automatically as if to touch that oddly bumpy brow or perhaps test the sharpness of those teeth - until he catches himself, and pulls it back, grinning a little self-consciously. All at once, he looks very young.