This is a reference to the rectum. The rectum is supposed to be situated on the western side of the eyes, nose and ears. This gate is especially meant for death. When an ordinary living entity abandons his present body, he passes through the rectum. It is therefore painful. When one is called by nature to evacuate, one also experiences pain. The friend of the living entity who accompanies him through this gate is named Lubdhaka, which means greed. Due to our greed, we eat unnecessarily, and such gluttony causes pain at the time of evacuation. The conclusion is that the living entity feels well if he evacuates properly. This gate is known as Nirrti, or the painful gate.