Tip: Keep the motion go through the whole body. This includes the tail. Like a string laying on the ground, when you wipe one end up then down. That motion flows down the length of the string and you see a wave. The tail in your animation is stiff and just looks out of place. When one thing looks out of place the whole animation brakes. So practice making it flow.
Here is a slow motion cat (Couldn't find a mouse but a cat is close enough) for reference. Watch how the the tail flows. When the base raises the tip lowers, as the base lowers the tip raises. ~[link]
Thanks for the tip! I knew the tail looked a bit strange, but to be honest I was kind of lazy and didn't put much movement into it. If I did I would have re-animated it on a new layer. But it is just a WIP after all. =3