The viscera effect allows your intestine's to spill forth from your stomach. Pressing the action button will make Sabitsuki attempt to put them back in to no avail.
The viscera effect can be found in the Flesh Walls world by navigating through the world and reaching a room with a dead black haired girl laying on the floor. Interacting with her will grant you the effect.
This effect is really hard to find since everything looks the same, and it's also very hard to write down. There was someone else who has made a walk through in which they described where to find it here: !!! Scroll down to the Viscera effect and follow. They might be using a different direction than the list above.
- The effect is ないぞう in Japanese.