facebook "seen message'?

[Davidson Bock]

I message a girl late at night on Facebook, next day, all day, she has been on several times, didnt respond, i did not see the check mark 'seen message', is there a chance that check mark has disappeared or something, i dont know how the message system works, could she be ignoring me or hasnt seen my my message
we were messaging before, but then what i described happened

[Ash]

You can look at the message in your message drop box without actually opening them. So maybe she did that, and just didn't open it.