That alone should have warned her that something wasn't quite right, but despite being so academically successful, Sarah was still just as error-prone as any other human.  "N-now you listen here!" she told her, stamping her foot down in emphasis.  "You get out right now, or I [i]will[/i] call the police!  If this is some prank or something, then consider me pranked and go home!  I have way too much to do to deal with this right now!"  She would have been alerted a long time ago if she were getting a new roommate, so that very likely wasn't the case - the lack of any items but her own (minus the other girl's book) was further evidence for that.  So she was either a burglar (and a rather poor one at that), or this was some silly prank set up by Jess or some other person on campus.  Either way, she had no time for it.  "Now please leave!" she said again, still pointing at the door.