Kaiba turns his back to Ferroc and shuffles on his way. It is perhaps a subtle sign that he really doesn't fear him, even if he could take his head off with a swipe of his claws. Maybe he thought he could defend himself. Or maybe he sensed that lack of destructiveness. Maybe both.

"You're not gonna cough up a hairball in there, are you?"

And maybe he couldn't help but troll. He won't kill the cat, but he may as well kill time.