A woman walks into a pharmacy and asks the pharmacist for arsenic.
The pharmacist then asks what she needs it for, to which she replies: "I want to use it to poison my husband.
The pharmacist says "Ma'am, I can not give you arsenic for that reason."
The woman then pulls a photograph from her purse and hands it to him. It was a picture of two people having sex; the man in the photo was her husband and the woman was the pharmacist's wife.
He then says, "Oh I'm sorry, I didn't realize you had a prescription."