When Guy pulls back his bow to fire the arrows falls out just before the shot is cut. When it cuts back to Guy the arrow is loaded back in the bow.
Before riding off, the Sheriff says to Guy, "Don't let them escape before I get back," and Guy replies, "They'll be dead by then." At this point both the Sheriff and Guy think that only Robin is in the tree and won't find out until later that Marian is there as well. Therefore they should have said "him" rather than "they" or "them".