The phrase "as still as a mouse" is often used to describe silence or a lack of movement. There are many synonyms for this phrase that can be used to provide variety in language and description. One alternative is "as quiet as a pin drop," which similarly emphasizes silence. Another option is "as motionless as a statue," which brings attention to the lack of movement. "Hushed as a library" works well in a context where a calm and silent environment is ideal. "Soundless as a tomb" can be used to invoke a more ominous atmosphere, while "silent as the grave" is similarly spooky.