No longer smiles
When it happens
Late severe stage
Why it happens
As muscles become more rigid, forming a smile may become a physical impossibility.
What you can do
Offer your touch. Just because you don't see a visual response (or hear a verbal one) doesn't mean the person has no reaction to loving kindness.
Offer your words. Most people with late-stage Alzheimer's can still hear (if they're not physically deaf due to another cause). Sing, talk, hum.