I agree with everything Beloz, Newsfie and K&P have said.
The reason Jack would slink away is due to your body language. Simply saying the word NAUGHTY in a stern voice would be confusing, as your body language would not reflect the mood you were trying to create. The same as he would also probably wag his tail in delight if you said NAUGHTY with a giant grin on your face and showed delight, because he can read the body language of happiness. It is a lot easier for you to realistically give off happy vibes to Jack because you love him. Not so easy to give off angry vibes when you’re not really angry with him.
The reason Jack slinks away when you say the word NAUGHTY, when he has done something “wrong”, is because every time he hears that word with that particular inflection coupled with your body language you grab him and put him outside. He is slinking away to avoid being caught and put outside. Just the same way dogs “learn” the words ‘good girl’ and ‘yes’. They don’t think, ”Yeah, I’ve been a great dog. They’re telling I was good for not ripping apart the outdoor furniture today”. They think, “every time they say “good girl” I get a pat. WOOHOO!!” or “Every time I hear “yes” I get a treat. It must be in their hand!!”, making them happy because they can predict a reward is coming. Just like Jack predicts the punishment is coming.
There was a study conducted (I can’t remember who by) where owners and their dogs were placed in a room with a treat on a plate. The owners were told their dog was not allowed to take the treat. The owner would leave the room and then come back in. The researcher would tell the owner whether or not the dog ate the treat and the owners would react accordingly (annoyance/anger if it was eaten, happy/praise the dog if not eaten). The researcher would randomly take away the treat. When the owner came back in they were told their dog ate the treat. The owners reacted and the dogs responded to the body language with (what humans perceive as) guilt. Researchers put treats back on the plates of dogs that had eaten the treat. The owners were told the dog didn’t eat it. The owners reacted accordingly and the dogs responded with happiness. And of course they had the control group. This study successfully proved that the dogs were only responding to the owners body language and did not understand that their behaviour was wrong and therefore feel “guilty”.
Sorry for the long post, I hope it made sense and gives everyone something to think about