She pushes him down and he's momentarily confused, hands sliding off her shoulders, until he realizes what she's doing (and where she's going) and then he's all at attention, focused as he can be under the circumstances. "Beckett..." What's that tone? Hesitation, readiness -- gratitude? They've done this dance in the dark before, but somehow, now, Castle's worried that he might not measure up. Then her mouth is on him and he thinks, good boy, before he groans around the feeling.