A mouse (rodent).
Source: http://www.nigms.nih.gov/NR/rdonlyres/89908011-CCC4-4A12-BC08-BC64FCA62DF8/0/mouse.jpg at http://www.nigms.nih.gov/Initiatives/Models/ (formerly at http://www.nigms.nih.gov/research/modelorganisms.html). http://en.wiktionary.org/wiki/File:House_mouse.jpg
Author: unknown