Arsenic

A woman walks into a pharmacy and tells the pharmacist, " I need some
arsenic. "

The pharmacist asks, " Why do you need arsenic? " The lady responds,
" I want to kill my husband. " The pharmacist says, " I'm sorry
ma'am, I can't give it to you for that reason. " The woman then
pulls out a photo of a man and a women in a very compromising position
and shows it to the pharmacist. The man in the photo is the womens
husband and the women in the photo is the pharmacists wife. The
pharmacist then says, " I'm sorry ma'am, I didn't realize you had a
prescription."