Brussels sprout
vegetable
Could someone mistake the smell of your brussels sprouts for a fart?
Brussels Sprouts are cruciferous vegetables. Cruciferous vegetables have a sulfur containing chemical called glucosinolate in them When you cook brussels sprouts, their smell intensifies. 
What kind of vegetable are brussels sprouts? What chemical is found inside #1? What happens to #2 when you cook them? Does #3 smell like farts?