"Stop what?" James asks, and the grin on his face is almost predatory now as he steps in to close the distance that Scorpius puts between them. "I'm not doing anything. Sort of offended you'd accuse me of as much, I told Al I'd behave."
It doesn't occur to him that Scorpius's reaction might be to anything but fear of being tossed into the water, or of being hexed - he was a strange boy with a thing for his brother, not him.