Because computer mice are designed to be ergonomic and not as small as they can possibly be, they contain a lot of unused space. While others have tried to enhance mice with LCD screens and label printers, a Swiss company called Pat Says Now worked on something simpler and created a mouse containing a floating rubber ducky in some paperweight-style water. It's low-tech kitch inside a high-tech USB attachment that's actually useful.
For those who prefer fish, the company makes a koi version as well. The "desk pets" cost $30.