This is a great question, and it’s true that the mechanics of the digestive system are quite complex. Let’s break down the question into a few parts.

• Is it possible to pass stool through the gut without expelling gas through the anus?
  • In most cases, it’s unlikely for stool to move through the intestines without pushing some gas in front of it. However, it’s possible to have bowel movements with minimal gas expulsion if there isn’t much gas in the intestines to begin with or if the gas is being absorbed into the bloodstream and expelled through the lungs.
• How could something push through a hollow tube as the intestines without pushing air out?
  • If you think of the intestines as a simple hollow tube, it might seem strange for solid matter to move through without pushing everything in front of it. However, the intestines aren’t simple tubes. They have various segments, valves, and sphincters that help manage the passage of content. Also, peristaltic waves—rhythmic muscle contractions—move material through the intestines. These contractions don’t simply push everything in front of them; they’re more coordinated and can move material in a segmented manner. So, while stool might push some gas along, it might not push all the gas out of the anus.
• What about the gas produced by bacteria?
  • Much of the gas in our intestines results from bacterial fermentation. Bacteria in our colon break down carbohydrates that haven’t been digested in the small intestine, producing gases like methane, hydrogen, and carbon dioxide in the process. If these gases aren’t expelled, they can accumulate and lead to discomfort.
• What if there were no bacteria in the gut?
  • Even without bacteria in the gut, there would still be some gas. This is because we swallow air when we eat and drink, which can introduce gases like nitrogen and oxygen into the digestive tract. However, without bacterial fermentation, the overall volume of gas would be significantly reduced.
• Would it be inevitable to fart due to the motion of stool?
  • The presence of stool moving through the intestines would likely cause some gas movement, but not necessarily result in a fart. Some gas could be absorbed into the bloodstream and expelled when we breathe out, while other gases might be held back by valves or sphincters until later.

In summary, while it’s improbable to have a bowel movement without any gas expulsion, the intricate design of the digestive system, with its valves and coordinated movements, means it’s possible for stool to move through with minimal gas expulsion.