When we receive a hit we breath it out but if we cannot breath because we are gagged, chocked or underwater we need to use movement to let the strike move and clear out. Start by breathing normally and having your partner stop you at any time according to what he sees as right (too much air, too little or anything that catches the eye) now start by pushing and as you hold your breath you move just enough to move the hit out, down or up and away. Keep this until you cannot hold your breath anymore and than change places. Do this for a while and than do a few rolls to clean the body of accumulated tension and repeat the drill using hits. Build this slowly to avoid harming each other and allow yourself to move freely without judgement to find out more about your movement under tension. This is not a complex drill but simple is not always easy.