A guy enters a pharmacy and asks for a vial of cyanide. The pharmacist, attempting to keep up a professional posture, asks the man what he might need it for.

"Oh," replies the man, "I want to poison my wife."

"I'm sorry, sir," the pharamcist says, "but you must understand that, under these circumstances, it's impossible for me to sell you the cyanide."

The guy immediately reaches into his wallet, pulls out a picture of his wife and quietly lays it on the sales counter.

Blushing, the pharmacist politely remarks, "Forgive me, sir, I didn't realize you had a prescription."