Stroke Buddy

I have one. We have never spoken.  He is maybe 40 years old, clean-shaven, always nicely dressed, clearly on his way to a job and a life. He has a hand that doesn't work and he limps a little.  Occasionally I sit across from him on the Red Line T (subway).  He sees me, there is recognition, a slow hint of a smile, and he bobs his head in acknowledgment.  My head slightly bobs back. We understand each other.