When your fart opens your anus releasing a wad of air while producing no noise.This fart can either be stinky or have no smell at all. If your stomach hurts than your fart will be hot and smelly.
I just farted and it was open-anus. My stomach hurts..did you smell it?
While at the office, casually walk over to a co-worker as if you have important news. When their guard is down, drop trousers, and in one motion, spread your ass-cheeks as far as possible with your hands and bend over releasing pure gasseous matter directly into the unsuspecting victims face. AKA: OBH (open butthole fart)
I couldn't believe it when Josh open-anus farted right in the middle of the office. His ass was right in my face.