The external anal sphincter is truly an amazing structure. Working in conjunction with the central nervous system, it can distinguish the presence of gas from liquids or solids in the distal end of the digestive system, thereby permitting the voluntary (most of the time) release (or not) of any of the foregoing states of wastage.
For example, say you’re sitting around with friends and Mr. Sphincter determines that it is dealing with the presence of gas, and you feel that you might be able to release the gas unnoticed. Accordingly, your brain instructs Mr. Sphicter to open the gate and let the gas pass.
The problem is that sometimes Mr. Sphincter gets it wrong.
Note: This post is dedicated to my friend, the late, great Acidman, who would have posted this in a heartbeat.