Comment by asdff
You have a back door as well for the gut that tends to open at least once a day. We know fecal matter is in the air in most bathrooms. It wouldn't surprise me if you got an infusion of community fecal biome right into your anus every time you used a restroom that isn't your own.
Yes but usually when the back door opens things are exiting the gut rather then going in. So I don’t think that counts.
There are cases where things do enter the back door but I think that’s just humans getting creative and it wasn’t designed for entry.