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Years ago, before the invention of weedeaters, we had gas powered edgers.
I had inherited my grandfather's which was made sometime in the early 60's. It had a pull start, and the way to kill it was to use your foot to push a lever up against the plug. I was having issues trying to get the drive belt to track properly, and after replacing belts, shims, washers, etc I fired it up.
It ran approximately 15 seconds before it threw the belt. Angry, hot, sweaty, and ready to give up on the idea, of having well trimmed lawn edges, I grabbed the handle in one hand and used my thumb to push the kill switch lever forward. I came to my senses about 10 yards away, feeling like someone had hit me in the chest with a 2x4.

I can definitely sympathize with the OP, but I agree, a practical demonstration is a very useful teaching opportunity.

I have a weedeater now.