鼠

It referring to rodents in the Muridae family.

It is a pictograph modeled after the teeth and body of a rat.

The character clearly mimics the shape and features of a rat, especially its teeth, head, and body.

At the top of the character is the component 臼 (gu, meaning “mortar”), which can cause confusion, but 鼠 is an independent radical (not derived from 臼).