First CNC scene

After a couple months with my dom and lots of discussion and trust built. I think we are finally ready to try our first CNC scene. So my question to my fellow subs - what is one thing you wish you knew prior to your first cnc scene?

Obviously there will be lots of communication, safety procautions etc. But I know I have blind spots even with lots of research. So I want to hear about your experiences and what you wish you knew before entering this kind of scene.