A married couple have been stranded on a deserted island for many years.
One day, another man washed up on shore. He and the wife became attracted to each other right away, but realized that they must be creative if they are to engage in any hanky-panky.
The husband, however, is very glad to have the second man there. "Now we will be able to have three people doing three eight hour shifts in the watchtower, instead of two people doing 12 hour shifts."
The newcomer is only too happy to help and in fact volunteers to do the first shift. He climbs up the tower to stand watch. Soon the couple on the ground are placing stones in a circle to make a fireplace to cook supper. The second man yells down, "Hey, no screwing!" They yell back, "We're not screwing!"
A few minutes later, they start to put driftwood into the stone circle. Again, the second man yells down, "Hey, no screwing!" Again, they yell back, "We're not screwing!" Later, they are putting palm leaves on the roof of their shack to patch leaks. Once again the second man yells down, "Hey, I said no screwing!" Once again they yell back, "We're not screwing!"
Finally the shift is over and the second man climbs down from the tower to be replaced by the husband. He's not even half way up before the wife and her new friend are hard at it. he husband looks out from the tower and says, "Son of a bitch. From up here it DOES look like they're screwing!"