1. have sth down to a science 精通某事。My grandma has cake-making down to a science. 奶奶特会烤蛋糕
2. rocket science. 高深之事。In order to stay healthy, you need to eat well and exercise. It's not rocket science. 良好饮食加锻炼才能有好身体，这不是什么深不可测的事。