A woman walks into a pharmacy, looks the pharmacist straight in the eye and says, "I would like to buy some cyanide."  

The pharmacist asks, "Why in the world do you want some cyanide?"

The woman replies, "I'm going to poison my husband."

The pharmacist's eyes get big and he exclaims, "Lord, have mercy!  I can't sell you cyanide to kill your husband!  That's against the law!  I'd lose my license!  They'd throw us both in jail!  All kinds of bad things would happen!  No, I cannot sell you any cyanide!"

The woman reaches into her purse and pulls out a picture of her husband in bed with the pharmacist's wife.

The pharmacist looks at the picture and calmly replies, "Well, now, that's different.  You didn't tell me you had a prescription."