He's not really thinking of Joker's toxin in particular so much as of thinking how to counteract anything really nasty that comes out of the shop and, which is more in his line, really, have the knives start turning into chocolate a few days after being bought. An enchanted stone in the scanner, maybe, or the door.
He shakes his head. "Not without being more visible than I'm prepared to right now. It's a matter of waiting, and maybe raising the stakes, until he tries to destroy me again." This smile is not a cheerful one at all, and not even bloodthirsty. It's just a little grim, and very, very tired. "This time I'll expect him."