Okay, so, I'd be lying if I denied my penchant for real inflation: it was the natural successor to my recently more realistic approach to the fetish (btw, if this is breaking the rules or something, please feel free to correct me).
Which of course, got me thinking. The people that do it tend to either inflate via the back passage, or stuff (or otherwise fill the stomach) via the mouth.
Now we know that human organs can only hold so much - last time I checked, about 4 litres for the stomach, and 9 for the colon. Both make one pretty big if filled.