what happens with the first and second stroke

In Fitt IV, the Green Knight, huge and formidable as before, meets Gawain with a monstrous axe. He welcomes Gawain, praising him for maintaining his part of the agreement and asking him to remove his helmet, so the exchange stroke can be received. The horrified Gawain exposes his neck, but at the last moment, he flinches from the axe and the Green Knight stops to yell at the cowardly Gawain. Gawain promises not to move the next time, but the second attempt stops short as well, enraging Gawain.