So they don't smoke what do they most likely do instead? They drink. So here is what you do get real drunk with them one night so they don't suspect anything get a shot of booze ready and poison it. Put as much rat poison as you possibly can in it. Now you say what if they don't drink? Well if they don't drink they are probably religious. Take their trusted theology book and cut out the inside of the book like you would to hide a flask. Then place pressure sensitive explosives inside of it. So next time they pick it up they get a wonderful surprise. Now you ask what if they aren't religious and they don't drink? Just shoot em in the head they are making it too complicated. When you read the title did you do a double take?