Testing can go on that list.

Very important in gauging where you fit in and peoples motives. Its done very discreetly because honestly in replies is the utmost importance.

There are many different reasons why its done, be it a response from them either by their body language or a simple comment ... or if its something i have said that has triggered my after thoughts into thinking "you idiot.
Either way its testing for acceptance and how long you have before you need to act like the phantom and vanish.