back to back..!!!

Robinson came home in great excitement and said to his wife, "You'll 
never believe it, dear, but I've discovered an entirely new position
for lovemaking."
"Really," said Mrs. Robinson, interested at once. "What is it?"
"Back to back."
"But that's crazy. We can't do anything back to back."
"Yes we can. I've persuaded another couple to help out."