This guy was filming the aftermath of an accident on I-80 in Sacramento, CA when something else drew his attention.
Other cars in the oncoming lane had been slowing down and paying more attention to the accident on the other side of the road than to the traffic in front of them, and a few cars ended up rear-ending each other.
They were rubbernecking. Rubbernecking is when people gawk at something of interest, and it happens a lot with car accidents. It is hard to pull your attention away from something like this, but doing so divides your attention and leaves you open to getting in your own accidents.
Unfortunately, one accident leads to another in this scenario and in less than a minute a handful of cars become involved. Remember, pay attention to the road, not something going on across the meridian.