"Oh." The acknowledgement takes far less time, and is far less surprised. Della's isn't the first missing limb he's seen (here, or at all), and whether people choose to talk about their injuries is up to them - he's not about to pry.

He's quiet for a moment as he tries to follow along with the story - this explains her prosthetic, but not why she thinks she's a bad mom (which he still doesn't believe for a second). "Did you make it home?"