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.
There are two most commonly used types of CV joints: a ball-type and a tripod-type. In front-wheel drive cars, ball-type CV joints are used on the outer side of the drive shafts (outer CV joints), while the tripod-type CV joints mostly used on the inner side (inner CV joints).