This question originally appeared on Quora: What are flight attendants really thinking when they are forced to greet and thank passengers at the door? Answer by Gaea Peregrinor, flight attendant.

I’ve been a flight attendant for 25 years. Greeting passengers at the door requires concentration on several levels. Of course the objective is to make you feel welcome and comfortable, but that’s only one aspect. While I’m trying to give that impression, I’m evaluating you very closely, and I’m considering a number of possibilities:

Is this person intoxicated?

What attitude do I get from this person? Helpful? Belligerent? Withdrawn?

Is this person physically fit? Powerful? If so, where is he/she sitting?

Any physical disabilities or hindrances such as a limp, injured hand/arm, etc.?

Traveling alone? With one other or with a group?

Comfortable/fluent with English language?

All of these things help me to assess people who can be helpful to us on a flight or even if they might develop into a problem. Remember that we will be hurtling through the air between six and seven miles above the earth. If a problem develops, one cannot simply dial 911 and wait for the police,so the whole idea is to prevent problems from getting airborne, and be prepared for them if they do develop in flight.

Obviously, if someone appears to be intoxicated, we don’t want them on the plane; the potential for future problems is too great. Likewise, if someone boards the plane with hateful and nasty attitude toward the crew, that’s a concern that needs to be addressed before departure. (It’s rare, but it has happened.)

I watch for disabilities that may disqualify someone from sitting in the exit row. They need to be able to physically lift a heavy hatch (up to 60 lbs) or open a heavy door (several hundred pounds). Likewise, if they cannot understand English, they cannot understand shouted commands, nor can they read the instructions on how to open the exits.

If I see someone who is muscular, powerful, strong, physically fit, I memorize his/her face and make a mental note of where they are sitting. I consider this person a resource for me. In the event of an attack on the flight or on me, these are my “go-to” people. If a situation looks like it could develop, I’ll privately and discreetly ask one of these people if they would be willing to help us if necessary. Help might involve subduing or restraining an unruly passenger. We hope it never happens, but we will prepare just in case it does.

I try to learn if we have any passengers who are airline employees, particularly crew members who have been trained in the in-flight procedures. These people also are a resource for me. They’ve been trained in what to do in an emergency—whether medical, mechanical, etc. They know how to handle the situations as well as I, and are trained to become an instant “team member,” fitting right in immediately if needed. When United flight 232 crashed in Sioux City Iowa in 1989, it was a disaster that should have killed everyone on the plane. But when the problems began, the head flight attendant remembered that an employee, a pilot, was riding in the coach cabin. She told the captain, who told her to ask him for his help. It was his assistance in the cockpit that helped save so many lives.

Consider that air travel is fraught with inherent danger, made more so by the political climate of the world today, one must be constantly alert and aware of one’s situation. When I greet people, you better believe that I’m always very aware of each passenger who steps through the door of the aircraft. And the items mentioned above are only a few of the myriad of “triggers” that we watch for. For example, I’ve had passengers board who look pasty and pale, deathly ill. (We removed them; nobody wants their flu germs!) I often see passengers who are afraid of flying and need a word of comfort and encouragement. I’ve had people try to smuggle pets in their purses or handbags, and bottles of booze in their briefcases. (Booze is allowed as long as it stays capped. You just can’t drink your own liquor on the plane.) So yes, I need to be vigilant and aware, all behind my “greeting face” of smile and pleasant, comforting welcome!.

As for thanking people as they leave, I’m probably thinking about getting out of my uniform and relaxing in the layover hotel, or at home! Or, I may be trying to figure out if I have enough time to grab a sandwich on my way to the next flight. Or, I may be figuring out how to get to my commuter flight home (I work in San Francisco but live in Denver.) Once I had to think about the furious drunk guy who was waiting in the boarding area for me to come out. He was angry because I had cut him off during the flight (he could hardly walk), and was determined to “have it out” with me. As it turned out, he sat down in a seat in the terminal to wait for me and passed out!

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