The NRM, or non-reinforcement marker, is very useful with a dog
who has a bit of clicker experience. It's usually a verbal marker,
such as 'uh-uh', spoken in a neutral tone of voice, which tells
the dog that he's got the behaviour wrong and he won't be getting
a reward. It is not a punishment, and you should under no circumstances
shout at the dog or appear angry. The idea is to give him some information,
namely, that the behaviour he has just tried isn't going to get
him anywhere. In our example, if the dog were to lift his head up
instead of turning it to the side, you could say a quiet 'uh-uh'
to tell him that he's on the wrong track and needs to try something
different. They get the idea remarkably quickly!