People often think (believe) that, experience, or they look like their rib cage is a solid or semi-solid object, and they think it was meant to have little or no movement.
But actually, since it is made up of so many separate parts (12 vertebrae, 11 discs, 24 ribs, 12 cartilages, 1 sternum, 1 xiphoid, 107 boney joints, 1 heart, 2 lungs, multiple fluid vessels and nerves, 1 esophagus, many muscles, and multiple layers of connective tissue), it has got to be one of the most flexible areas in the the body.
If you will just locate each of the joints in your thorax and add a little movement to each of them, then you will find great freedom of movement in your chest. You will breathe better and have greater vital capacity (breath, blood and lymph flow, digestion, etc.). This movement will add more flexibility to the rest of your body, since your total movement patterns are limited to the degree that the least movable area will or will not move.
Exercise 1: Go to an an anatomy book and locate joints in the thorax. Place your finger tip or tips over the are of each joint in turn. Walk, move, roll, explore movement in that joint area as this and other parts of your body move. Go slowly, go gently, be attentive and you will learn and surely increase awareness and movement in this and all areas of your self, even increase movement in the brain.