I've noticed that after I've talked to a girl who seemed interested in me, but whom I did not escalate with beyond the initial conversation, will avoid eye contact with me during chance encounters. If a girl I've talked to before comes out of the door of a building I'm walking to, she will turn her head at a 90 degree angle away from me as if to scrutinize something. This also happened two days ago with a girl who I've never met, but who usually stares at me like a deer in headlights whenever we pass each other on campus.

It seems that when a girl is very interested in you, she will turn cold if you don't return her interest soon enough. I wonder if these girls are still on some level attracted.