"Ow," says Jack, wincing descriptively.

No, he didn't need that tailbone, thanks for asking.

He starts to roll very stiffly onto his front, so it's evident that he hasn't broken his spine or anything so dramatic. But still, it was a jarring and painful shock. And furthermore ow.

Jack opts to grit his teeth and avoid making any more pained noises.

That's really the only reason he's not calling Sinclair a collection of names that would give his fake mother the vapors.