When my dad was in a nursing home, we used to bring our basset Elvis to visit him. It took us forever to get to my dad's room because *everyone* wanted to say hello to Elvis. And Elvis, a typical friendly basset, had to stop and say hello to everyone. I can still picture his tail waving even while we were still out in the parking lot, in joyful anticipation.
Some of the people who were withdrawn seemed to come out of their shells when Elvis stopped by.
I had another friend who was sick and in an assisted living. His dog was the only one who could get him to eat! For every bite the puppy got, my friend had to eat one.