The sulfur is not directly a gas :) It is usually in the form of other gaseous compounds which contain thiols (-SH), and hydrogen sulfide; another smelly compound is the nitrogenous compound Skatole it is a large part of why some farts smell like "rotten eggs". Additionally farts smell like shit, because they literally contain nanoparticulate poop pieces. When you smell someone elses fart, you are physically breathing in a small amount of their poop. Gross.