That’s a really interesting question. I’m going to start by saying that everyone’s body is different, so there may not be a universal answer to this question. However, I can tell you about some of the possible explanations for why someone might not pass gas when they have a bowel movement. One possibility is that the person’s digestive system is working very efficiently, so there’s no excess gas being produced in the first place. Another possibility is that the person has a strong sphincter muscle (the muscle that controls the opening of the anus), which prevents any gas from escaping.