As a rule, Foster does not hold reality to a lot of expectations. Some of it could probably be attributed to the presence of magic as an everyday occurrence in his world, but... that actually has very little to do with it.

And yet Lapis not only manages to surprise him, she manages to briefly alarm him--or at least make him kick, spasmodically, legs splayed like he anticipates the need to struggle, or maybe swim. It's little more than pointless flailing, honestly.

Which again sends pain radiating from his hip, which makes him kick harder, and--well, anyway, she's not drowning him or even doing anything interesting and eventually he stops. But really, he hadn't even grasped what Lapis was doing, let alone why. Foster's instincts lean more towards taking the opportunity to drown himself than... anything to prevent that.

"I know Amethyst is a gem," Foster complains, frustrated.