An 80 year old couple decide they want kids again. They visit the doctor who suggests, since they are a little older than usual, some tests might be in order. He hands the couple a small jar and asks them to go next door and for the gentleman to fill it so they can test his sperm count.
A few minutes later the couple returns and hands back the jar. The doctor exclaims, "But it's still empty!"
The main replies, "I know. I tried with my right hand, I tried with my left hand, then I tried with both hands, and I still couldn't do it.
Then my wife tried with her right hand, then her left hand, and with both hands. She tried with her teeth in and her teeth out.
And we still couldn't get the lid off that jar!"