Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Works Perfectly

I have a 5 month old lab mix and it worked perfectly on her. She would bark for hours on end when I was gone, and I put this on her one day and she's not barked since. Will not work on small dogs (she's over 30 lbs.) and sometimes when she shakes, it will move so that it won't work anymore.Overall, it's been wonderful. I only had to use it a couple times and she learned very quickly not to bark. I highly recommend this.