Still in the rodent category but cuter :
Quiet as a mouse.
Nervous as a mouse in a room full of cats.
The Mouse ran up the clock, hickory dickory dock.
Then, there is Aesop's "The Lion and the Mouse" with its famous line "No act of kindness, no matter how small, is ever wasted."
If that's not enough, then how about : "The Town Mouse and the Country Mouse" with its observation : "A crust eaten in peace is better than a banquet partaken in anxiety."
Finally -- lest you think I have abandoned the main topic : check out Robert Browning's poem "The Pied Piper of Hamlin" which mentions more rats than you can shake a stick at! wow