We never think about some of our body parts. Most of us don't consider what our kidneys are doing unless they malfunction; we rely on them to do their job without any mindful action on our part.
Other body parts are heavily invested with emotional meaning and metaphor. "It's out of my hands." "I need to get something off my chest." "I can't stomach this." "I don't want to tread on anyone's toes." "It's a millstone around my neck." "I'm shouldering the burden." "This is a pain in the neck (or backside)." "My heart is broken." Oh, that heart! I haven't counted, but I'm pretty sure there would be more metaphorical sayings about hearts than for any other body part.
But when we the last time you thought about your tongue? I tried to think of some metaphors involving this particular body part, but could only come up with four: "Bite your tongue!" (or "Hold your tongue!") as an admonition to keep outspoken speech to yourself, "The rough side of your tongue" for harsh words, "It's right on the tip of my tongue" for when you can't remember something, and "sticking out your tongue" as a rude gesture.
Whatever the imagery, the meaning is clear: your tongue is something you're supposed to keep hidden, as if some authority has instructed us "Don't let that thing out of there! It's meant to stay on the inside!"
While we certainly rely on the tongue's presence for speaking, eating, and romantic kissing, most of us cellists probably aren't thinking much about it when we're playing an instrument. Unlike woodwind players, brass players, and singers, the tongue doesn't play a huge role in our instrumental technique.
Or does it?
In Cello Practice, Cello Performance, I wrote a lot about the role of breathing in playing the cello, both in terms of bowing technique and left-hand techniques such as shifting. In Chapter Two, I wrote some exercises on these subjects, and observed "Breathing out through the nose...will help you 'breathe through' the resistance of your bow's hair against your string when you play." (pp. 11-12)
If human breathing is analogous to bowing and tone, the human tongue is analogous to bow changes, articulations, and the character of our expression. If bowing and vibrato are how we sing on the cello, articulations and bow changes are how we speak. It makes sense that the body part we associate with speaking and eating--the basic motions that keep us alive and communicating--should have some physical and emotional part to play in cello playing.
Physically, I've discovered that it's impossible to be relaxed if my tongue is tense. Try tensing your tongue, and you'll notice that it makes your jaw, mouth, and neck tense. If those parts of your body are tense, it only stands to reason (since body parts are connected) that this kind of tension will manifest it in your shoulders, hands, and arms when playing the cello.
Emotionally? Well, consider the expression "Bite your tongue!" It implies biting back hasty words and angry feelings, suppressing them, keeping them on the inside...
...which is funny, because that's exactly what happens to your feelings for music when you're tense. All those carefully planned expressions? They can't come out because the physical constraints of playing the cello tensely won't let them. Expression might be "right on the tip of your tongue," but it's not getting any further out of your mouth than that--or out of your cello.
I confess I hadn't thought much about what my tongue was doing inside my mouth while I was playing the cello until recently. But I had a couple of students who were having trouble making a resonant tone in spite of working on the breathing and Infinity Symbol exercises from Cello Practice, Cello Performance. I had them trying all the tricks I knew, but I wasn't getting to the heart of the problem. So I consulted some singer friends and started reading vocal pedagogy websites, hoping that voice tips on sound production might help. After all, I always have students sing their repertoire away from the cello, since if you can't sing it, you can't play it.
Then I started reading about jaw, mouth, and tongue tension. Most of us already know not to clench our jaws and pinch our lips together when we play the cello, but when I read about the role of tongue tension in vocal technique, and it was like the missing piece of a puzzle. Of course! Why hadn't I been asking my students about tongue tension when we were addressing other tension issues?
So, how does this work? How can we use our tongues to improve our relaxation, and by extension, our sound?
Here are some of the ways we found:
1. Completely relax your tongue inside your mouth. Your tongue is a muscle, and like other muscles, if you can feel it, it means you're tensing it. Try to get to a place where you can't feel your tongue. If you're struggling to do this, try placing your tongue at the bottom of your mouth behind your lower incisors and sing "Awwww" until it relaxes. (For a comparison, sing "Eeee" and notice how it tenses your tongue.)
2. Now practice some long tones and slow scales on the cello, breathing deeply in through your mouth and out through your nose, as explained in Chapter Two of Cello Practice, Cello Performance. Listen out for your most resonant sound, adding vibrato. Pay mindful attention to what your tongue is doing. If you "forget" and let your tongue tense up unthinkingly, simply draw your mindful attention back to it and notice how much your tone improves when it's relaxed.
3. Start playing a piece of music that you know well. Let your hands and arms "flow" as you play, and think only of the balance, equilibrium, and relaxation of your tongue.
4. If you experience tension in any other part of your body, draw your attention back to your tongue. Is it relaxed? Notice how your tongue's relaxation can influence other parts of your body to relax.