The size of the sabretooth relative to humans keeps changing.
When the Sabretooth attacks the young couple in the cabin, it pulls the man through the door, leaving a hole. Later the hole is seen again, but is smaller.
When the Sabre Toothed Cat escapes, he is shown breaking the cage by slicing the roof with his teeth. This is impossible, because Smilodon fatalis is known for having large but fragile teeth. This is true for all members of the Machairodont subfamily.
All the characters, including Casey and other supposedly experienced mountaineers, repeatedly make greenhorn hiker mistakes: exploring an unknown cave for "fun" in mountain lion country; splitting up to look for a dangerous animal; leaving camp perimeter after dark; etc.
A man manually removes a steel jaw leghold trap from his ankle, which would be impossible for him to do alone..
Bricklin carries a moderately sized backpack and is the only person in the group of three carrying a pack - yet he manages to bring a huge three person tent along with everything else the group needs. There is no way he could possibly carry that much gear in that size of a backpack.
When kicking the board in half it can be seen that the board is already broken just before it is kicked.
The "abandoned mine", large enough to have elaborate wood framing, is high in the mountains, at least "four hours hike" from the trail-head at high altitude. Mines, even abandoned ones, are always located near some kind of negotiable road. Otherwise the ore could not be extracted.
Vanessa Angel plays an American, but her accent and British mannerisms keep slipping through.
Casey dumps Lola's snacks into a trash can which is not bear proof.