scratch someone's back
原文解釋: to do a favor for someone in return for a favor done for you
1. You scratch my back, and I'll scratch yours.
2. We believe that the mayor has been scratching the treasurer's back.
3. I do have some information you might be interested in,
but what can you offer me in return? You scratch my back and I'll scratch yours.
4. I'll grab the box on the top shelf if you will creep under the table andpick up my pen.
You scratch my back, and I'll scratch yours.