Bertholdt is yanked into the water with a small noise of surprise. Even as he falls in, he's laughing, though. He's a strong swimmer, firstly, and he's also Winterblessed.

Which he immediately makes use of to keep himself afloat, squinting at Reiner playfully before he smiles very slightly... and a small wave of water swamps Reiner from behind. Guess who's in his element right now, landlubber.