Indeed, it would probably be better if he didn't; Katie would surely have noticed and gone nosing around Loki entirely and possibly bowling him over with her nose if he had.
Sif didn't register the leash twist, at least. Small favors? She was still smiling. "First one you've asked about," she pointed out. "You must like her. The answer is that no, I don't, but you might try my shoulder bag -- she'd notice if I handed it to you, I'm sure, but, Mr. Sleight-of-Hand, I trust you can make it seem to the horse as if you've materialized fruit from thin air."
Because Sif's bag was, in fact, holding a couple of fresh apples.