By AJ Willingham

CNN

(CNN) -- By now, the video of a United passenger being dragged off a flight at Chicago's O'Hare airport has made it around the world and undoubtedly inundated your news feeds. There are a million things to unpack about the incident: The appropriate use of force, the rights of passengers, the PR fallout and ultimately the state of air travel that allowed for such a thing to happen.

But if you just need to get caught up, here are the biggest questions people are asking:

1. Why this man?

According to multiple passenger accounts to CNN, United was looking to free up four seats on Sunday evening flight from Chicago to Louisville in order to accommodate United employees who needed to be in Louisville for their shifts. After offering passengers $800 to disembark, a flight attendant announced that the plane was not going anywhere until the four seats were surrendered. They then announced they had chosen four people at random to remove from the flight.

Except, according to airline spokesman Charlie Hobart, it wasn't completely random. Hobart told CNN that United weighs a number of factors to determine who is chosen to leave the flight, such as connecting flights and how long of a delay the passenger will have at the airport. United's carriage contract also provides some guidelines for who can and cannot get the boot -- unaccompanied minors and people with disabilities, for instance, should be removed only as a last resort.

Other airlines have their own criteria. Delta, for instance, will not remove members of the military and will give special consideration to passengers enrolled in loyalty programs.

2. Who is he?

The identity of the passenger who was seen screaming and later being dragged off the plane with blood on his face has not yet been released. The Chicago Police Department says he is 69 years old. Passengers said he told flight attendants and law enforcement that he was a doctor who could not afford to be re-booked because he had patients to see the next day.

Passenger Tyler Bridges told CNN in an interview that the Sunday evening flight was the last one of the day to Louisville -- the next available United flight there wasn't until Monday afternoon.

The man is also believed to be Chinese, which has caused huge controversy in China, one of United's biggest markets. A passenger told CNN the man was overheard saying he was profiled for being Chinese.

3. Can an airline legally kick a paying customer off a flight?

Actually, yes. According to data from the Department of Transportation, 46,000 passengers were involuntarily bumped from flights. This happens because most carriers purposefully overbook their flights knowing people sometimes won't show up.

When an airline chooses to clear out seats on a flight, they are required to go through a process: First, according to the Department of Transportation, they have to see if anyone will give up their seat voluntarily. They typically offer compensation, such as a voucher for another flight.

Also, as mentioned above, while airlines can legally kick people off, each airline has its own general guidelines as to who they kick off and why.

4. Why didn't they just offer the man more money? '

This is one of the biggest questions people have about the incident. According to passenger accounts, United's offer for compensation stopped at $800 -- a rather small sum for such an expensive inconvenience, and certainly not a sum worth the amount of ire United has faced in the last few days. According to DOT regulations, there is no "mandated form or amount of compensation that airlines offer to volunteers."

"Carriers can negotiate with their passengers for mutually acceptable compensation," the regulations read.

Now, where it gets really interesting is when passengers are bumped involuntarily, like the four people on Sunday night's flight. Depending on the length of the delay, the airline may have to pay $1,350 for the inconvenience.

"If the substitute transportation is scheduled to get you to your destination more than two hours later (four hours internationally)... the compensation [is] 400% of your one-way fare, $1350 maximum."

That maximum would fit United's predicament, since the next scheduled flight to Louisville was a full day later.