Hydrogen sulfide

There is more information available on this subject at Hydrogen sulfide on the English Wikipedia.

3D Structure of hydrogen sulfide

Hydrogen sulfide, chemical symbol H₂S, is a colorless, toxic, and flammable gaseous chemical compound responsible for the foul odor of rotten eggs and flatulence.

When the Engineers resort to anaerobic digestion for food, bacteria in its anaerobic sacs convert the organic material to energy. This process gives off trace amounts of hydrogen sulfide.