A husband and wife stuck on a desert island take turns climbing the only palm tree in search of a rescue ship. One day the husband calls out, "Helen, a man on a raft is approaching." When the man arrives, they tell him their story and that they are glad he is there because now each needs only to lookout for 8 hours instead of 12. The new man climbs the palm and after an hour he calls down, "Hey, stop fucking down there."
The husband and wife look at each other perplexed and call back, "We aren't fucking."
The next day the man is on his watch in the palm and calls down, "Hey, stop fucking down there."
Again the husband and wife shake their heads and answer, "We aren't fucking."
The next day the husband is up in the palm, looks down and thinks to himself, "You know , it DOES look like they are fucking down there."