Another trick, stuff a potato up the tail pipe, two for duals, you cant start the car because there is not enough air flow. I taught that to my son. He had a professor at UF who was an arrogant ***. She didnt show up for any classes the next day.
Heard of that never tried it. But one I have used on a Mechanic that bragged he could diagnose any problem. Take a pencil and draw a line inside distributor cap from coil wire to ground very tuff to see without a flashlight