Revealing mistake: Watch the scene where they're headbanging and the tape keeps going out. You can see where they splice the scene in because the trees change in the background instantly.
Revealing mistake: After the roof blows off the cabin, the hail starts falling inside the cabin. It is fairly obvious that the hail is just being poured onto the cabin. Its most noticeable just after the hail starts falling on the cabin, there is a shot taken from inside the cabin you can tell by the night sky and some of the trees outside that there is no hail in the distance.
Revealing mistake: When it starts hailing inside the cabin, you can obviously tell that the night sky has wrinkles in it, revealing that this "sky" is a black curtain in a stage.
Revealing mistake: Could the scene when the big rock knocks down the cabin be any faker? You can easily tell that the cabin and the rock are miniature models.