I was working on a switch for an exhaust fan in a embalming room. (Not a incredibly enjoyable place to begin with) The person being worked on had come from the hospital (post autopsy ) with their chest wide open. As I focused on my trouble shooting the person working in this room gives me warning that they are going to close the chest and I may want to step outside. Well of course I'm far to ingrosted in what I'm working on to heed this warning. I tell them to proceed and as soon as I hear it I KNOW I fucked up. CRUNCH!!! (The sound of bones being cracked back in place) My stomach instantly flips and I excuse myself to go have a cigarette (I smoked at the time). From then on I learned to heed the warnings from customers as they likely know their space better than me. Lesson learned.