In the UK, there is something called "passing off" and it's illegal. In short, if your mouse looks too much like Stuart Little, the copyright/trademark holders may complain that you are trying to pass off your creation as their work and will be annoyed. If your mouse is sufficiently different to their mouse so that there can be no confusion, then there is no problem.

Mike

PS: Would anybody like to buy a Carter watch or some Hugh Boss aftershave? My local market sold both (before the Trading Standards people moved in).