In the moments before the spell, Faelan had to struggle not to scamper backwards, but somehow he didn't think Sirius would like that well at all. There was a sharp instinct from deep inside of him to bare his teeth, to growl at the threat that Sirius' eyes represented. But when their gazes held, the wolf backed down in the space of a blink.
When the spell took hold, the wolf was weakened. It roiled in shock, a feeling coming over him like the rushing of blood from every far-flung vessel to the center of his heart, exploding not with anger or feral ferocity, but desperation. The wolf cried, a twisted howl emerging as it fought, clinging with all its might to Faelan's every bone.