Arsenic

A woman walks into the drug store and asks the druggist for some arsenic.

The druggist asks "Ma'am, what do you want with arsenic?"

The woman say's "To kill my husband."

"I can't sell you any for that reason," says the druggist.

The woman then reaches into her purse, pulls out a photo and shows it to the druggist. The photo is of a man and a woman in a compromising position, the man is her husband and the woman is the druggist's wife.

He looks at the photo and says "Oh.......... I didn't know you had a prescription!"