>>855234well as long as the ass and the mouth belong to the same person you should (somewhat) fine.
Minor infections may occur in rare cases but you will not get crazy diseases from it since the bacteria that are going back in are the persons own gut bacteria.
As long as there are no open cuts or scratches in the mouth its pretty safe. Its a lot safer then ass to vagina.
this being said does not mean its not gross, its still disgusting to do and I assume it tastes terrible.