When two of the characters are kissing on a bed, the movement triggers a trip wire to ring a bell in Jacob's room. The first time we see the bell ring, it is the big one on the top row of bells. When the trip wire is activated again moments later by the same couple on the same bed, we see that a smaller bell on the bottom row of bells is ringing.
In the opening scene, the two officers step out of their cruiser and head towards the church. We see clearly one has sergeant stripes, yet when they reach the door both clearly have captain bars.
While Jacob is trying to break open the elevator door with his axe, the chop marks are not only different on either side (interior/exterior) of the doors, but the interior also shows the axe marks disappearing and reappearing again.
The tattoos on Michael's hands disappear then re-appear in shots. In close ups they're visible yet in long shots they've vanished, despite the lettering been large and black.
In the movie they explain that there was a fire on the penthouse level, and you can see that in the scenes, but if there were in fact a fire, the wiring would not be able to hold a current without shorting, yet there are lights on in the penthouse.
In one of the last scenes, when one of the women has the ability to shoot the murderer, the pistol is suddenly empty. The Glock pistol that was used is a semi-automatic weapon that uses the recoil of the last shot to load another bullet. If the last shot is fired the breech block slides back and won't slide forward again as seen in the movie. She (and the audience) would have been able to see that there is clearly no bullet left in the pistol instead of recognizing it after pulling the trigger.
In an early shot, in the trailer park, garbage and waste is shown everywhere. One shot shows a close up of an old newspaper. On the paper is visible in bold print HOLDEN which is the Australasian wing of GM, in fact the HOLDEN badge is also partly visible. Also, but not so obvious, also printed is the name of the Brisbane suburb Wynnum.
In one of the penthouses where the teens have joined to smoke pot, upon the lighting of the second joint, the camera zooms out to show all four teens and a very visible boom mic. A few moment later, it's shown again.
While Margaret is in bed reading the newspaper, a boom mic can be seen lowering down toward her in the overhead shot.