He recognizes the change in her expression and demeanor, because it's something he has seen in the mirror and felt in himself. It's a hard, abrupt gear change. Maybe a mask or persona being pulled up, maybe an outright lie. He doesn't have enough information to confirm or dismiss that, yet.

Something similar happens to him, but there's no shuttering, not overtly, just his expression and tone lightening up. Becoming...playful. He doesn't feel playful, but he can meet what she's giving him very, very easily. It's very nearly habit.

He laughs, quiet and - light - and starts to walk backward (facing her, moving toward the building). "Funny thing. Would you believe I seem to have misplaced it? And I haven't seen an ATM either? I can't imagine why, really, but I'm afraid dinner may be a less lavish affair than either of us are accustomed to. I'm sure I'll think of a way to make it up to you."

And that's more words than he used at once on the wall. Playboy is a whole hell of a lot more verbose than Batman. Or even Bruce.