why camel spit alot

Many animals have ways to tell others to stay away when they are defending their food or protecting  themselves. If they can convince animal or person to keep its distance, then they avoid fight.
This type of communication can be different for different kinds of animals. A bird may screech and dive at your head if it thinks you are too close to its  stomach contents into its mouth,mix them with saliva and spit at you.Thats a plenty clear signal back off.