Onions, cabbage, garlic. While nutritious, eating these foods can lead to an embarrassing side effect: smelly flatulence. More than just smelly, hydrogen sulfide, the chemical compound responsible for the rotten-egg aroma, is deadly if inhaled at doses of more than 700 parts per million. (Thankfully, a bout of flatulence contains just .001 to 1 ppm sulfide.)
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Source: Phys.org