Scratch and scrimp
Basically, you do something for me, I'll do something for you.
Both are in fact true. The real way of saying it is to scratch an itch, but you can also say that you itch a scratch.
A Scratch Is: A scratch is a mark on your body that could be coused by hiting somthing, or taking your finger nail and rub it hardly aganst your skin. As a verb: When you itch, you feel something...
Scratch is the interpreted dynamic visual programming language based on and implemented in Squeak