Cyanide

Lady walks into a drug store and tells the pharmacist she needs some cyanide.

The pharmacist says, "Why in the world do you need cyanide?"

The lady then explains she needs it to poison her husband.

The pharmacists eyes got big and he says, "Lord have mercy", I can't give you cyanide to kill your husband! That's against the law! I'll lose my license, and they'll throw both of us in jail and all kinds of bad things will happen! Absolutely not, you can NOT have any cyanide!"

Then the lady 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 replies, "Well, hell, you didn't tell me you had a prescription."