Dogs have long memories ....
I bought some skiing equipment from a store some 2 years ago where they had a quite old labrador. She recognised me immediately as soon as I walked into the shop about two weeks ago - luckily by wagging her tail. Confirmed by the owner that she only ever got up to greet customers she knows.
It is therefore to be hoped that the placing of the towel will be seen as an act of friendship in the longer term
Put a large towel gently over your dog's head.
If he extracts himself within 15 seconds, he's highly intelligent.
If he takes 30 seconds, he's average.
If he walks around bumping into things all day with the towel on
his head, don't get too upset: who wants a dog that's smarter