This required some closer examination. You were right about the flocking, which only looks like felt, and it is a two layer card. But Santa's sleigh really is attached -- I was able to slide a bit of paper behind it. And it's not plastic, it's actually some type of metal, heavier than aluminum. So it certainly could have damaged a machine canceller. Fortunately, this was mailed in a tiny town (about a hour's drive from my home) for city delivery, so it got a hand stamp.