
To be honest you need to think about the fact that the judge needs to assess the dog in limited time.
So if you think you will save time by stopping and then resuming like with when a dog is moving incorrectly, (playing up or pacing etc) it is better to start again, rather than try to do the whole movement pattern only for the judge to have to waste time asking you to do it again as they can't asses the movement.
a lot of pups will scratch at the collar simply as it is restricting them or making pressure to make them go where you want, and they either don't like it or are not that used to it, and try to stop the sensation or you getting them to do something by scratching.
I had a problem with Lexi with her shaking her head if there was any pressure on the lead, and my present pup will try to scratch.
the answer is really to have a loose lead and the dogs attention.