The interaction between Mary and Dean is making him grin for some reason he can't explain. It's nice to see him this close to happy for once, especially after everything that's happened lately.

Toby's just catching the tail end of Dean's direct thought when Mary asks that question, and with that timing, he doesn't think right off that she's talking about anything else. He looks back at her, mouth opening hesitantly, and glances at Dean.

"... Ah..."