I suspect many people have a visceral reaction to dog shit, baby shit, and any kind of shit. And pee. That milk carton in the refrigerator. A backed-up toilet, dishwasher or garbage disposal. A restaurant grease trap. Woof, that smell. That is disgust. The revulsion. This was a useful, evolutionary survival mechanism to make sure the cave dweller didn't eat something that will kill the tribe. Don't eat it, don't smell it, don't even look at it. This isn't fear, anger or sadness, it's disgust.