Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Harmful

The problem with a prong collar is people keep them on the dog 24/7. It is mearly a training tool and the goal should be to have the dog work on the flat collar. Please don't use this unless you know how to use it. This device can cause nerve damage on your dog. See if you can find the book "No bad dogs, no bad owners.