Lets just say this straight: you can vomit poo out of your mouth. If youre lying in a funny position at this moment in time, move right now with immediate effect. The official name for this is copremesis. Bowel obstruction can cause your gastric muscles to contract, pushing faecal matter up and out. So next time you're vigorously doing sit-ups, just remember that youve got at least a couple of pounds of poo sitting in your digestive tract thats just dying to explode out of your mouth in a scene reminiscent of The Exorcist.