Why do farts smell?

Someone ask: Why do farts smell?

Caveman say fart smell because belly tribe make gas and tiny gut beasts make stinky bits too. When food get broken down, some sulfur-like stuff and other smelly chemicals ride gas out. Same as rotten eggs or swamp mud, small bad-smell pieces can travel far in air even in little amount. Most fart gas itself no smell; odor come from sneaky chemicals mixed inside. Foods like beans, cabbage, and meat can feed gut beasts in ways that make more stink. Cave wisdom: sound may warn tribe, but smell is gas carrying tiny invisible messengers.