I have no shortage of these, I’m pained to admit. Here are a couple:
When I lived in California, I had a gimmicky little tchotchke called Earthquake in a Can. When sitting on a desk, it looked just like a regular canned item. But when you picked it up, some gizmo inside caused it to shimmy and quake like anything. Being a natural practical joker, I quite enjoyed watching the reactions of visitors to my office when they casually picked up the can and it did its thing.
When I left the job, I didn’t disable the battery-operated mechanism, just shoved the can into a box along with my other personal items. Put the box in my trunk. Forgot about it.
A week or two later, I noticed a strange shimmy in the rear of the vehicle every time I made a left hand turn. It felt just like something mechanical had started to fail! I took the car to my trusty mechanic. It took him two days and the assistance of his son riding in the trunk of the car while he drove to discover the problem.
I paid him his hourly rate and changed mechanics, due to extreme embarrassment.
More recently, I purchased a rear tine rototiller for my gardens. I carefully studied the schematic on the machine that showed the gear configuration. Everything worked as pictured, except the reverse tine rotation. The tiller kept moving forward, not in reverse as I expected.
I called the dealer’s service department and they kindly offered to send a fellow along after his regular work day to take a look. He ran the tiller through its paces and pronounced it was working perfectly. I pointed out that the tiller moved forward even when the tine rotation was set in reverse. Just as I said it, the penny dropped. What kind of idiot expects the tiller to move in reverse just because the tines are rotating in that direction? This idiot, that’s who.
All I know is, every time I stop by that tractor dealer, they always remember me.
Aspenglow, not an engineer.