I also thought it was novel, but I have a different perspective now. I was editing the Polish part of our trip last night and looked at this shot pretty hard. I now believe that the snake is not real, and is used to keep birds off the windowsill. I made 6 shots of this guy in about 10 minutes, and the snake did not move or change positions during that time. The guy moved some but the snake did not. The other thing is the guy's windowsill is much cleaner than the windowsills of the adjacent windows. Lastly, the "snake" looks similar to the Kingsnake found in the US.

I am not positive, but if I had to bet, I'd bet on a fake snake. I'll never know for sure, the guy might just have a different preference in pets than most of us, and cleans his windowsill once a week

Edit: djb contacted his friend who is knowledgeable about snakes (see post below), and her verdict is that the snake is real. It is a Kingsnake held by an experienced handler.