https://online2.tingclass.net/lesson/shi0529/0009/9907/629.mp3
https://image.tingclass.net/statics/js/2012
behind one's back 在某人之背后,背着某人,背地里
They did it behind Mike's back.
他们是背着麦克做的这件事。
What? You ate up everything behind my back.
什么,你居然背着我把所有东西都吃光了。