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.
What's wrong with a car when you put in drive, and it stalls out? A CV boot covers and protects the drive-axle joints that allow a car to turn right and left and to go forward or backward with its front wheels. They hold the grease that keep the joints lubricated and operating smoothly. Replacing a worn, cracked CV joint is a relatively easy and inexpensive repair.