speak volumes (about/ for sth. / sb.)

　　单单某一件事就很说明问题，不需要过多的解释(to tell you a lot about sth./ sb., without the need for words)。比如：

　　His achievement speaks volumes for his determination.

　　What you wear speaks volumes about you.

　　overbite

　　嗯，这个就是我们在形容某人长相时，偶尔会用到的“龅牙”(a condition in which a person or animal's upper jaw is too far forward in relation to their lower jaw)。比如：

　　She was a fifth-grader when she got braces to correct an overbite and a gap between her two front teeth.

　　on your mind

　　If sb. / sth. is on your mind, you are thinking and worrying about them/ it a lot.

　　当我们下回想说“有心事”的时候，就可以用起来了。例如：

　　Don't bother your father tonight—he's got a lot on his mind.

　　You've been on my mind all day.

　　上面的这个是说“我一天都在想你”，你在我脑海里挥之不去，这个意思还可以说成I just can't get you out of my mind.