Hey there and thanks for asking! When looking at Rule #14's mention of extreme violence, I would draw comparisons better with movies. You'd want to steer clear of graphical stuff like in the Saw/Hostel franchise, while completely over-the-top violence (like in Peter Jackson's Braindead/Dead Alive) maybe given more leeway.
Ultimately, though, you need to remember Rule #19. The judges have sole discretion to disqualify based on their interpretation of the rules. Therefore, if any of the four judges decide that your game breaks the extreme violence rule, then your will be disqualified. You wont be able to argue the semantics of Rule #14, even with what I've told you in the paragraph above.
In short: I recommend you steer clear of your gross-out idea, but if you feel that you can do it without crossing the line, go for it!