Hit space to crash you're screen. If you have a Chromebook like me, It will not let you click anything, and It will eventually show what the thumbnail is. Reload to restart you're screen.
To crash the screen, I made a "run without screen refresh block that makes 300000000000 clones of yourself. When space key pressed, the block will run. When you start as clone, you go to a random position, and run the block again. Because of Scratches clone limit, when it exceeds it quickly, the screen crashes instantly.