A supplement to the 2002 version of Big Eyes, Small Mouth (BESM 2.5). It covers numerous templates for insects and animals and updates to the BESM 2.5 rules to allow for diminutive creatures.
From the website:
They lurk in the shadows, invisible to the powerful and arrogant eyes of man. Nothing is too small to escape their notice. Silently, they lay their intricate, complex plans. Carefully, they place their rubber-band catapults. Tonight, the cheese will be theirs! The first BESM supplement to be inspired by American animation and comics, Big Ears, Small Mouse takes players into the strange but familiar world of Mousetropolis, with talking rodents, bugs, and other tiny animals. Beware the cat.