Okay, some of you may not know, but you should NEVER get under a car that is held up only by a jack. You should chock the rear wheels, put the car in gear, put the e-brake on, and use JACK STANDS. If you want proof of why you should, just read below.
When I jacked this car up to install my ladder bar, I left the jack snug up against the car as a back up to the jackstand, just out of paranoia. Well five minutes into the install, in the back of the below picture, you can see the jack has slowly leaked down to a couple inches lower than the jackstand. If that car was only held up by a jack, I would have been slowly crushed.
Just FYI. Lol.