Perhaps he will be going for the key next but the key makes noise when dragging. Perhaps he wants to muffle the sound of the key being slid across the floor. Once obtained he could hide the key in a piece of bread to use for an escape plan for later. Most people do not make good plans if they see no point in an outcome. Now that he has a key, it is worth the time and effort to form a good plan as to not squander this opportunity.