Good point. The boom is difficult to work out where it comes from. I short cycled the bolt on my 375H&H once and failed to pickup a round (I'd just gotten out of the car and was trying to be real quiet) - the dry fire click sent the pig into high gear.

Another time I was driving along a bore drain when I spotted a pig on the other side and up a ways a bit. I killed the engine and left the key in the ignition, with the intention of closing ground on foot (and in stealth mode). I'd only recently bought this car (Jeep) and didn't realise all the "features" it had. As soon as I opened the door, a chime started going off (to remind me of the key in the ignition). Piggy took off quickly.