Literal translation: The hills shook, a mouse was born
Meaning: Something important is about to happen. You are expecting something big, worrying, anticipating and fearing. You have big plans and hopes. And then a mouse is born. Nothing of substance really happens. This phrase is meant to gently poke fun at someone who is making a big deal out of nothing.
Use: When someone is losing sleep over an exam, whines about how they are going to fail, contemplates quitting school and moving to Nepal to become a Buddhist monk, shaves their head the night before and then the exam is cancelled.