Flight attendants may seem chipper and carefree, but dont be fooled: While pouring bubbly and chatting with travelers, these trained first responders are also keeping a close watch over the plane for threats, starting the very moment you board.

Passengers think we are just greeting them at the door, Jay Robert, a flight attendant and founder of Fly Guy , told HuffPost. But theyd be surprised at the number of threats we eliminate at that stage of the flight which would have caused a delay or even harmed their health and safety.

We asked flight attendants to name the first thing they notice about passengers when they board a plane. Most of their answers have less to do with judging your in-flight look and more about keeping you safe. The right boarding behavior could score you better service, too. Heres what the cabin crew notices:

If you look them in the eye.

[I notice] who makes eye contact with me and who doesnt. More often than not, the ones who dont make eye contact make me investigate... Are they scared of flying? Are they feeling okay? Are they dealing with a personal issue? These are things people dont tell you outright, and a facet of my job is making sure everyone is having a comfortable flying experience. Stephanie Mikel, Southwest Airlines

If youre drunk.

Intoxication and aggressive passengers are prime suspects we try to identify at the doors. We are trained in basic taekwondo techniques to handle acts of aggression in the sky, but stopping them before they get up there is our main goal. Jay Robert of Fly Guy

If youre in shape.

Im looking for able bodied persons who can assist with security problems inflight, as well as someone who appears willing and able to assist in an emergency evacuation. Typically, this is someone who is traveling alone and in street clothes, looks like they are in above average physical shape or is known emergency service personnel. Zac Ford, flight attendant with a major carrier