Saliva collecting on the lips of a human baby. It mostly comes from salivary glands in the cheek.

Saliva is the watery substance made in the mouths of humans and many animals. Saliva begins digesting food in the mouth, and moistens food to make swallowing easier. Saliva consists of 99.5% water.

The mouth is obviously the point of entry to the whole alimentary canal. It follows from this that saliva must both help digestion, and protect against infections.