"Visiting Mars" joke

After accumulating sufficient frequent flyer miles, Bill and Bernice landed on Mars where they met a Martian couple. They were talking about all sorts of things and Bill asked if Mars had a stock market, did they have laptop computers, how they made money.
Finally, Bernice broached the subject of sex. "Just how do you do it?" she asked.
"Pretty much the same way you do," replied the male Martian.
A discussion ensued, and finally the couples decided to swap partners for the night. Bernice and the male Martian headed off to a bedroom, where the male stripped. After taking one look at him, Bernice was disappointed to see that he only had a teeny, weenie member, about half an inch long and a quarter inch wide. "I really don't think this is going to work," Bernice said.
"Why not?" he asked. "What's the problem?"
"Well, it's just not long enough to reach me!" she explained.
"No problem," he said, as he proceeded to slap his forehead with his palm. With each slap, his member grew until it was quite an impressive length.
"That's very impressive," said Bernice, "but it's still pretty narrow."
"No problem," he replied, as he started pulling his ears. With each pull, his member grew wider and wider.
"Wow!!" she exclaimed, as they fell into bed and made mad, passionate love.
The following day, the couples rejoined their normal partners and went their separate ways. As they walked along, Bill asked, "Well, how was it? Was it any good?"
"I hate to admit it, but it was pretty, darn wonderful," replied Bernice. "How was it for you?"
"It was horrible!" groaned Bill. "All I got was a headache. She kept slapping my forehead and pulling my ears!"