Scary. If I had been a passenger I am certain my first reaction would be to jet, and I might have begun to ... but would redirect and attempt something in aid of the victim. I have been in crazy situations (well, not this crazy) and have helped so I know how I react in panicked scenarios.
However, I don't fault those who chose to bail on the gruesome scene. I mean, that is some wacky stuff. Dude's stabbing like a machine and then decides to cut off his victim's head. Wow.