She brought her knees up into his back, but one might have had more success hitting a waterbed.  The effect was the same. Beneath his skin, which was tougher than one might guess, his skeleton, muscles and organs all sat in a sea of viscous fluids.  His skeleton, he’d learned, was more like a shark’s than a human’s.  It was a flexible cartilage that bent where bone would break, and healed faster than bone.  He’d been hit by a car and climbed to his feet shortly after.  Her kicks would not have much effect. - Interlude 5