The Sages taught in a baraita: A person has two kidneys; one advises him to do good and one advises him to do evil. And it stands to reason that the one advising him to do good is to his right and the one that advises him to do evil is to his left, as it is written: “A wise man’s understanding is at his right hand, but a fool’s understanding is at his left” (Ecclesiastes 10:2). Tangential to the subject of kidneys, the Gemara cites that which the Sages taught in a baraita with regard to the roles of various organs: The kidneys advise, the heart understands, the tongue shapes the sounds that emerges from the mouth, the mouth completes the shaping of the voice, the esophagus takes in and lets out all kinds of food, the trachea produces the voice, and the lungs draw all kinds of liquids, the liver becomes angry, the gall bladder injects a drop of gall into the liver and allays anger, the spleen laughs, the maw grinds the food, and the stomach brings sleep, the nose awakens. If they reversed roles such that the organ which brings on sleep were to awaken, or the organ which awakens were to bring on sleep, the individual would gradually deteriorate. It was taught: If both bring on sleep or both awaken, the person immediately dies.