This is a video of some guys demonstrating how to jumpstart a car (or a cah if you're the man filming the clip) when you don't have jumper cables, but can take the battery out of another vehicle. It shouldn't come as any surprise that this works, since jumper cables are just the vessels through which electricity flows from one battery to the other when jumping a car using the traditional method. This is just cutting out the middle man. Is it safe? I wouldn't do it. Would I watch a friend do it while I sip a beer and scream 'BE CAREFUL' whenever he gets close to the other battery? I would actually pay to get to do that.
Keep going for the video while I miss Car Talk, where I first heard about people doing this. Also, I listened to the whole thing at 1/4 speed and I'm fairly certain I just unlocked the key to the universe.
Thanks to Tim M, who agrees if you really want a car to start you just have to threaten that you're going to push it into a lake if it doesn't start acting right.