Leader was climbing the second pitch of a multi-pitch route. Out of sight of the belayer. Leader got pumped and started down-climbing to his last runner. As down climbing and about to fall off due to pump he shouted 'Take!'. Belayer thought the leader was shouting 'Safe!' and so shouted up 'Off Belay!'. Luckily, the belayer's habit was to shout off-belay before actully taking the leader off belay. So the leader had time to shout back that he needed to take. Disaster averted, just.