The Scanning Electron Microscopy lab this semester was the most awesome, because after making a few hasty demonstrations, the lab assistant ran away and left us for dead for the rest of the day.
The lab report stated: You should NEVER try to operate it by yourself until you have reached a certain standard as judged by your demonstrator.
We LOL'd. We could not believe our luck. Then we proceeded to vent the chamber without turning off the electron beam.