I once rolled under my truck to jump the starter. Imagine my surprise when it started and I realized I had left it in gear.Had that happen to a Mercedes Diesel with a manual gear box. Service advisor left it in reverse after checking the reverse lights when I had already done so. Checking vave clearance with a jumper switch and the engine caught. Service advisor wasnt allowed to touch any cars while they were in the shop ever again.
I caught the car and hit the shut off switch under the hood befor any damage was done.