Compared to the two women (and Jack too, of course), the Doctor was in a far worse state. It was all well and good to have River jump him, at this point, but this? He didn't sign up for this!

While River was unabashed, the Doctor had furiously red cheeks as he just stared, wide eyed and gaping. After a moment it seemed like he was trying to say something but no sound came out. The only thing keeping him put was the fact that River was leaning against him, so instead he just nudged her side because shouldn't they carry on down the hall? Why were they stopping?