Mrs. Smith walks into a pharmacy and asks to buy poison
'Dear lady, why would you want to buy poison?' asks the pharmacist.
'To kill my husband!'
'I can't sell you poison so you can kill someone!'
As an answer to that, Mrs. Smith puts a picture on the counter where one can clearly see a man and a woman in bed. The man in question is Mrs. Smith's husband, while the woman is the pharmacist's wife. The pharmacist picks up the picture and nods:
'Excuse my mistake, I didn't know you had a prescr…