You CAN teach old dogs new tricks...or they teach themselves

So my dog Cocoa is 13 years old and not allowed to watch people while they eat.  This is a form of begging and he knows it is against the rules.  It has been this way for 13 years. 
Well, recently he started coming in my room while I was eating and he will start to stare, I will give him the look or tell him no, and he will turn his head, or lay down facing the other direction. 
Tonight when this happened I felt like someone was watching me so I turned around and when I looked over he was acting like he wasn't looking at me while I was eating, but he was intensely staring at me through my wall mirror!   It totally creeped me out!  I have never seen him do this before!  He has tried to be sneaky in the past by trying to look through his long hair when it is covering his eyes, or peering around a corner thinking we can't see him, but looking at people through a mirror, that is totally new and creepy. 

I tried to get him to look in a mirror when he was younger, just playing and he never seemed to get it.  Well apparently he was just "playing dumb" and us humans were the dumb ones.   I wonder what other tricks he has up his fur that we don't know about.