While farts are made up of several different gases—oxygen, nitrogen, methane, carbon dioxide, and hydrogen—it’s the hydrogen sulfide that’s responsible for making your wind smell like a carton of eggs left to rot in the sun. In order to discover how the gas interacts with feces, the scientists gathered the poop of seven healthy volunteers and then mixed it with components commonly found in both meat and carbohydrates to see which produced more of the odor-causing gas. While fart production might increase, fiber soaking up water in the intestine helps knock out the sulfide and reduce the smell.