A woman walks into a pharmacy¹ and asks the pharmacist for some arsenic².

Surprised, the pharmacist asks, "Madam, what do you want with arsenic?"

The woman replies that she wants to kill her husband.

Horrified³, the pharmacist says, "Madam, I can't sell you arsenic to kill a person!"

The woman reaches into her handbag, takes out a photograph and lays it down on the counter. The photo shows a man and a woman in a sexually compromising position. The man is her husband. The pharmacist recognises his wife as the woman in the photograph.

The pharmacist picks up the photo and nods, "Ah, madam, I didn't realise you had a prescription⁴."