Gasping for air while mouth half covered by water?

The game thinks in tiles as units. One tile can only have one material occupying it. His legs are in a tile occupied by water but his head is in a tile of air. While the animation cause shim to haunch over and lower his head, that's only visual. They also can't differentiate the depth of the water in less than one tile units. A full tile of water and a tiny layer of water is the same for the game, which is why you see a blueish mist over thin layers of water as it takes the whole tile, and also why liquids sometimes look weird sticking to the ceiling above them and such despite being only a little amount.