when you are leaning into the engine bay of your Wrangler working on the motor and you have a foot on either side of the front wheel. Then you have your GF turn the motor over to check something (she doesn't take ot out of gear or push the clutch in) and it rolls forward onto your foot. Then you go to move in that direction and it rolls back onto your other foot as she lets the key go because of the shock of the Jeep moving and your frantic screaming :-)