Recall the shape of the falling star’s face—it resembled Calcifer’s. Calcifer may have been a falling star, though the novel doesn’t confirm this yet. (Calcifer’s cryptic note that Sophie got her hint, though, suggests this is correct.) Howl’s angry reaction to the fact that Michael tried at all to catch a star suggests he may regret having caught a star himself once. The contract might not be helping him much, either, or his current relationship with Calcifer might not be as good as Sophie thinks it is.