quiet as a mouse

Adjective

idiomatic

(simile, idiomatic) Very quiet, so as to not be heard

Japanese Meaning

非常に静かで、音を立てずに目立たない様子 / 控えめで目立たない、非常に静かな状態

During the long church service, the baby lay quiet as a mouse.

長い礼拝の間、赤ちゃんはねずみのように静かに横たわっていた。

Sense（1）

(simile, idiomatic) Very quiet, so as to not be heard

（ alternative ）