be very careful when doing anything with the engine running!

I had my motor running with the car on stands, I was sitting with my legs under the car and grabbed near the grille opening to stand up. The thermo fan (it's a pusher in front of the radiator) kicked in and chopped off my thumb

Fortunately the surgeons put it back on, but it hurt pretty bad and no one was home to help at the time, so I drove myself to hospital (10 mins away). Rocked up to the hospital completely covered in blood, and waited for 7 hours with no pain relief in emergency... not fun stuff.