When Jordan climbs the ladder to the roof, closeups show her wearing flat/sneaker type shoes. Before and after, she is wearing boots with large square heels. This can be seen both times she climbs up to the roof.
Despite some of the gruesome methods used to murder the victims, there is never any blood spilled, which might have tipped off the other party goers.
At the end of the movie when Jordan shoves Nick off the roof, you can clearly distinguish the stunt man that lands on the car, and not the original actor.
At the end of the movie when Nick is chasing Jordan, he states "My lucky day, one shot left," after he's already fired the six rounds allotted for that revolver.