There is tremendous power in our thoughts. Those who use the biofeedback machine called EMP (Electro-myograph) find that the muscle tension of one's muscles changes, even before one says something. Just thinking about saying something immediately changes the tension of the muscles. Your muscles constantly emit electrical energy that is measured in micro-volts (a millionth of a volt), and when you think of saying something that causes you tension, your muscles become tense and they give off more electricity. When you think of saying something that is calming and relaxing, your muscles immediately become more relaxed and give off less electricity. Anyone who uses such a machine can see the power of thoughts in action.
Note: Using a mirror isn't as sophisticated. But when you think thoughts and then look in a mirror, you will get visual feedback. Observe the difference in your facial expressions when you access negative and non-resourceful states compared with when you access joyful or serene states.
(Growth Through Tehillim: Exploring Psalms for Life Transforming Thoughts, p. 106)