Prescription

A lady went into the pharmacy, walked up to the pharmacist, looked straight into his eyes, and said, "I would like to buy some cyanide. 

The pharmacist asked, "Why?" The lady replied, "I need it to poison my husband." The pharmacist said 'Lord have mercy! that's against the law! Absolutely not!" 

The lady reached into her purse and pulled out a picture of her husband in bed with the pharmacist's wife.

The pharmacist looked at the picture and replied, "You didn't tell me you had a prescription!