[It could be that Sebastian knows himself well enough - and why wouldn't he, being as old as he is? - to know he won't take kindly to anyone or anything threatening Ciel right now. Not even a mindless forest creature. Of course he wouldn't cause a needless delay to Ciel's bath and fresh clothes just to take out his own possessiveness on an attacking monster, but... he's not really in the mood for quick and efficient. Better not invite the situation. And perhaps, perhaps he does enjoy how Ciel is forced to lean against him. His helpless little master who couldn't renounce Sebastian even if he wanted to...]
Young master? [He helpfully slows to a walk. Easier to talk that way, not to mention it will look less urgent to any passerby.]