This means that the receiving KNIGHT cannot look at a card he is receiving from his King before choosing the card he will give back. It also means that it is not possible to exchange a card with a Knight who has none to start with, nor for the receiving Knight to give back to Arthur the card he just received from him, as the exchange is simultaneous.
Il n'est pas possible de faire un échange avec un chevalier qui ne dispose d'aucune carte en main.