Why do our stomachs turn when we see/smell something gross?

What causes it?Why do our stomachs turn when we see/smell something gross?
it is a gag reflex that your body does when it requirements to throw up (mentally) but not physically. smiling is found to have suppresed the reflex
I would activity to guess that is is a defense works -- a way for your body to bring up to date you "do not eat".
It's a mental and physical spasm. It's your brain telling your body. "Oh this is not flawless, not good at adjectives, don't even thing something like eating it." It's animal quality.
Your body has several things it does to try to protect itself from outside organisms/bacteria and such that could wreak you harm. One of the things that can take place is when you see or smell something gross, your body sort of thinks that it cant be perfect for you and may cause you injure so your stomach starts to feel nauseated so that you won't stay around that gross point or eat it or touch it or anything.