Old people and nastiness

A very old couple wanted to have children, so they went to their doctor and told him their problem. The doctor gave the couple a tiny jar and told them to fill it up. About a week later, the couple came back.

"I tried with my right hand until it gave out, and I tried with my left hand until it gave out," said the man.

"And I tried with both hands until they gave out," said the woman. "And we still can't get the lid off the jar."