The Pharmacy

A woman walks into a pharmacy and tells the pharmacist "I'd like to buy some cyanide."

The pharmacist says " What do you need that for?"

"It's for my husband." the woman says.

"I can't sell you that. That's poison. Why do you want that?" says the pharmacist.

The woman rummages in her purse and shows the pharmacist a picture of her husband in bed with the pharmacist's wife.

"Why didn't you tell me you had a prescription?" asks the pharmacist.