What it is
The molecule that makes things taste of butter — sprayed onto microwave popcorn, margarine and snacks in place of actual butter.
Why your biology objects
A synthetic butter flavor with a notorious *occupational* hazard: factory workers inhaling its heated vapor developed "popcorn lung" (bronchiolitis obliterans). Eating it isn't the same exposure — the lung disease is from inhaling the vapor — but it's a synthetic flavor standing in for the butter the recipe didn't buy.