A prisoner in jail receives a letter from his wife.
"I have decided to plant some lettuce in the back garden. When is the best time to plant them?"
The prisoner, knowing that the prison guards read all mail, replied in a letter.
"Whatever you do, do not touch the back garden."
A week or so later, he received another letter from his wife.
"You wouldn't believe what happened, some men came with shovels to the house, and dug up the entire backyard."
The prisoner wrote another letter back to his wife.
"Now is the very best time to plant the lettuce."