One symptom of Parkinson's disease is a loss of facial expression

The late boxing champion Muhammad Ali, seen here with his wife Lonnie at the premiere of his screen biography Ali on Dec 17, 2001, exhibits the typical mask-like expression of Parkinson’s patients. — AFP

A simple smile can express love, affection and care for others better than any language on earth.

It shows happiness, promotes long life and is a free therapy for many diseases.