Final answer:
When Sir Gawain hits the Green Knight with the axe, the Green Knight's head is chopped off and reminds Sir Gawain of their agreement. This event is a pivotal moment in the medieval English poem Sir Gawain and the Green Knight.
Step-by-step explanation:
When Sir Gawain hits the Green Knight with the axe, the Green Knight's head is chopped off, but he picks up his head and reminds Sir Gawain of their agreement—Sir Gawain must seek him out in a year and a day to receive a blow in return. This event is a pivotal moment in the medieval English poem Sir Gawain and the Green Knight. It tests Sir Gawain's honor, bravery, and chivalry.