When a man and woman, man and man or a woman and woman get on all fours. They have to be ass to ass, all the while making sure the assholes align. Then one sexual partner tries to shit a fudge log into the asshole of the other. The stool sample must be solid in order to avoid a derailment.
I heard that your mom tried to give your dad a"Manhattan Transfer" but there was a derailment and there were no survivors.