So much blood from your body goes through the tongue, and not many people know that different areas of the tongue, reflect different areas of the body. The very tip of it, shows your heart, just over that is the lungs, and more, in fact the health of the major 12 meridians can be seen in simple-to-memorize map, so that you can, quite accurately, give a simple health diagnosis to someone. So the next time your acupuncturist says "put your tongue out", relax and just let that tongue hang out. They are being careful to check their diagnosis.