The man smiled a little, “Therefore it’s logical to assume you don’t masturbate often.”
“Never!” the builder exclaimed.
“Well there you have it” the man explained, “That’s logical science at work. From finding out that you have a goldfish, I’ve discovered the size of your garden, all about your house, your family and your sex life!”
The builder left, very impressed by the man’s talents.
On returning to the bar the other builder asked, “I see that smart bloke was in there, did you find out what he does?”
“Yeah,” replied the first, “He’s a logical scientist.”
“A what?” the puzzled second builder asked.
“Let me explain” the first builder continued, “Do you have a goldfish at home?”
“No” replied his mate.
“Well, you’re a wanker then!”

