I came across a guy on Reddit a while back who was currently employed at Facebook. He thought he'd try making a video of him doing one of Facebook's interview questions thinking it'd be easy for him to do. He stumbled through the problem and didn't end up solving it in the timeframe that would have been allowed.

It was good of him to still post it but it showed that someone currently employed at Facebook would have been screened out at the phone call stage had he applied again without any preparation.