I've seen it happen when a dog wants to nail something. I've seen it happen half way through work when they start to put the wood to something. I've seen it happen when the dog comes out of a nice warm house on a cold day like it was goose bumps.

When it comes to that kind of thing.... I recognize and acknowledge it like I would with any behavior but I don't judge it until after the fact. Maybe over time it will give me impressions of what is to come (are they starting to draw? Are they pulling up?) but right now I keep it simple and let them show me everything they have and not judge them prematurely based on fuzzing up, tails dropping, tails raising, even turning. Not every bad sign leads to a bad result, but they just may.