A middle aged couple went to a spouse swapping party. They met a Martian couple and thought it would be nice to switch partners for the night. So they went off with the opposite spouse.
When the woman saw the male martians penis she said "Well thats nice but its kind of short isnt it?" The Martian then reached up and patted his head. While he did that his penis got longer and longer.
The woman saw that and said "Thats nice but its not very fat is it?" The martian again reached up and pulled on his ears. As he was doing that his penis got fatter and fatter.
The women had a grand time that night. In the morning the man and woman were comparing their experience.
The woman said "I really enjoyed myself, we should swap again."
The man said "I enjoyed it too but, I just cant figure out why she kept patting my head and pulling my ears!"