This is a way of marking territory if they are rubbing the sides of their faces on the object. Cats have scent glands around their lips and on their chins. The facial pheromones that they mark with are signals of a happy or calm cat to other cats.
The part that simultaneously enables the axle to flex while transmitting the driving force is called a drive axle joint, and is also known as a constant velocity (or CV) joint. The CV Boot is a ribbed, rubber flexible boot that keeps water and dirt out of the joint and the special grease inside the joint.
Some vehicles even employ CV joint axles in the driveline. The CV joint of the axle is a collection of bearings and cages that the allow axle rotation and power delivery on a bunch of different angles and planes, and for the axle to change length as it travels up and down.