A lady walks up to a pharmacist and says "I need s

A lady walks up to a pharmacist and says "I need some poison." The pharmacist asks for what. The lady begins to tell him that she had been married for years, had been faithful and loving to her husband, but she began to have suspicions that he was cheating on her. So she hired a private investigator to follow and photo her husband in the act. The longer she talked, the more frantic and emotional she became. The pharmacist explains that he can't sell her poison for the purposes of killing her husband. The lady pulls out one of the pictures of her husband in the act with the pharmacist's wife. The pharmacists looks at the picture surprisingly and tells the lady "Well, you didn't tell me you had a prescription."