i bought my last rattie (r.i.p. fatty) a harness and she HATED!!! the thing so much..she was used to running around freely and then we put the harness on her and she looked so sad she kept on shaking, as if she was wet, trying to get it off..so we did our best to try and get her used to it! But one day she went into her paper & cardboard playhouse and took it off, some how, and we never did find the thing...even after we moved! such a lil cutie...but that let us know that she did hate it and to not use one with her!!!