A woman walks into a pharmacy, strolls over to the counter, and catches the pharmacist's attention. "Can I please get some arsenic?" she asks. "Arsenic? What do you want arsenic for?" asks the pharmacist.

"It's for my husband," she replies.

"Your husband?" exclaims the pharmacist, "I hope you don't mean what I think you mean!"

She just nods.

"Well, lady," he replies, "I'm an honest man. I can't sell you arsenic, I wouldn't if I could, and I don't know what made you think you could just stroll into a respectable store and expect me to sell you arsenic!"

She doesn't say a word. She just reaches into her purse, fishes out a photograph, and hands it to the pharmacist. It is a picture of her husband, in bed with the pharmacist's wife.

The pharmacist slowly looks up over the counter, and then straight at her. "Lady," he says, "why didn't you tell me you had a prescription?"