Automatic gear selectors look fairly simple from the outside. There's a lever with a release button that when pressed, allows the user to move between Park, Neutral, Reverse, Drive, and sometimes a low gear. But in reality, that shifter mechanism contains a whole bunch of stuff to keep it from shifting when the driver doesn't ask it to.
YouTube user put together this quick breakdown video showing us exactly what hides underneath all that plastic to make sure an automatic transmission shifter functions as it should. As it turns out, there's several pieces of clever engineering in place to make sure the lever doesn't slip out of Park, all working together seamlessly in a way that doesn't hinder the end user.
Even if you're not into the engineering aspect of it, the video's still interesting to watch since you get to see what the inside of a shifter actually looks like.
Take a look for yourself.