Hauling Harry out was like hauling a sack of bricks. He was weighed down by more than just wet clothes. The sword fell out of his grip as Ron pulled him out, and he struggled to breathe, hands coming up to claw at his throat, trying to pull the locket off.
His lips had gone blue - from cold or lack of oxygen or both, and his spectacles were half off his face.
He managed to get the locket away enough to drag in a ragged breath and he looked up at Ron, not entirely sure that he was actually seeing something real. Ron hadn't been there, after all. He was sure of that. He didn't know why he'd see Ron and not Nagini or something though. "R-Ron?" he choked out.
He swallowed hard and saw Nagini slithering away again in the back of his mind. He remembered what he'd heard too, now. A hiss of a word that no one else would understand, just praise for his pet. But it made Harry think. Before he could overthink it, or lose the image of the snake in his mind that would let him speak it at all, Harry opened his mouth, hissing out a breathless open in parseltongue.
The choking weight at his neck abruptly eased, and the locket, whose covering had come off somewhere in the water, opened.