This whole “rat poison” thing is simply deliberately alarmist. Coumarins have the aroma of vanilla, and are found naturally in lavender plants, strawberries, sweet clover grass, licorice, cherries, and cinnamon. These compounds have been literally used for well over a century as flavoring and scent agents in a variety of products from food, to tobacco, to perfumes

The amount used to scent tobacco is literally on the order of less than parts per million, meaning that to ingest a potentially harmful dose, a smoker would have to literally simultaneously smoke tens of thousands of cigarettes. If you are smoking those cigarettes, the LAST thing you have to worry about is sub-microscopic amounts of coumarin for scent!