A lady walks into the drug store and asks the druggist for some arsenic.
The druggist asks: "Ma'am, what do you want with arsenic?"
The lady replies: "I want to kill my husband."
"I can't sell you any for that reason," says the druggist.
The lady then reaches into her purse and pulls out a photo of a man and a woman in a compromising position - the man is her husband and the lady is the druggist's wife - and shows it to the druggist.
He looks at the photo and says... "Oh I didn't know you had a prescription!"