While Elliot is at the Diner with the dead body, the dead body's head is first down. Then, while Elliot is freaking out, at the same time the dead body's head is up again.
When Elloit is sawing off his old school bully's arm, the strap that holds said arm disappears during the more aggressive sawing, and then reappears before the arm has been fully seperated.
Around 1:07:00 Elliot gets a text message, and he pulls out the phone that he left behind in a dumpster only minutes earlier. He even stole someone else's phone. The original phone was a flip phone and the one he stole was a "chocolate bar"-style phone. Also the same message tone.
(At around 29 min) The "Ostrich" that they bring into the police station is an Emu.
In Australia, it is virtually impossible that a private security guard at a function such as a university dinner would be armed with a handgun.
At about 37:50 into the movie, the guy on the phone says "New Orleans Parish". There is no "New Orleans parish", It is just "Orleans" parish.
When describing Challenge #6, the Voice says, "Upstairs in 6-B lives Mr. Shaw, a lonely man." Mr. Brindle misses the opportunity to dispute this as a lie, since Mr. Shaw, being dead, is no longer living anywhere at all.