Last week, I had a ton of fun in our TCM practical staring at my classmates' tongues. We spent over an hour simply examining each others' tongues. There were ten of us in total and all ten tongues looked completely different. We went around in a circle, all taking a turn to have our tongue analyzed by the group and teaching assistant.
Some tongues were purplish, others were dark red, several quivered, some didn't stick out very far, there were cracks down the middle, and even prominent papillae (i.e. little red bumps on the surface of the tongue). Each of these tongue characteristics gives a clue as to what is going on internally in the body. Our tongue can be used to monitor our digestion, nutrition, stress levels, temperature, and more.
If you don't believe that you can get any information about your body's functioning from your tongue, I challenge you to start looking at your own tongue more regularly. Watch how it changes over the course of a week, or better yet, a month. When you feel comfortable with your own tongue, then start looking at other tongues (the tongue of your partner, best friend, or child... whoever will let you take a peak!). Be prepared to see a very different looking tongue staring back at you.