A woman walks into the pharmacy and say, " I would like to buy some cyanide."

The pharmacist, curious, asked, "What do you need cyanide for?"

"I want to kill my husband", she replies.

The Pharmacist apologizes, and says, "I can't sell you cyanide to kill someone."

" You don't understand, he's been cheating on me," she explains and shows a photograph of her husband in bed with another woman, who happened to be the Pharmacist's wife.

'Oh, I didn't know you had a prescription."