Human beings produce three basic types of tears: basal tears, which lubricate the eye to keep it clear of dust; reflex tears, which wash out irritants, like onion vapors, that come into contact with the eye; and psychic tears, which result from strong emotions or physical pain and have a different chemical makeup than those created for lubrication. Though tearing as an emotional reaction is considered by many to be a uniquely human phenomenon, some studies suggest that what animals cry too? Discuss
Source: The Free Dictionary