When Mick, Geri and Roger are out in the boat, Roger shows the two of them his bitten-off thumb. In the next scene, when Roger grabs onto the dock, both of his thumbs are visible.
When Geri and Mick first discover the skeleton, the skull is fragmented, with the jaw bone clearly disconnected. When they later find it in the back of Roger's truck, the jaw bone is now firmly attached and they have to forcibly pull it off.
When a worm slides down the wall behind Mick, it leaves a trail of slime that disappears in the next shot.
As Geri and a soaking wet-shirted Mick leave for the Beardsleys' house, and they get out of the car to follow an upset Roger, Mick's shirt is dry. When they join Roger and Willie by the truck, however, his shirt is soaking wet again.
When Mick and Jerry discover the skeleton, it has no sternum nor is its jaw attached. Later, after Jerry is fishing, he returns to the truck to find a complete skeleton. Furthermore, the skeleton in the dirt is female, while the skeleton in the truck is male.
When Mick gets off the bus at the washed-out road, the bus driver tells him his destination (Fly Creek) is "five miles straight ahead", but it is just half a mile if he cuts through the woods. This is physically impossible, since something five miles away in a straight line cannot also be half a mile away.
When Roger is attacking Mick for the last time (biting his thigh) and Mick begins hitting him with a flashlight, he is obviously hitting his own hand rather than Roger's head.
When Roger throws a board at Mick, it knocks Mick out and the board is clearly on top of him. When he wakes up, the board is off to his side.
When Mick is investigating the truck after getting off the boat and using his lighter as a source of light, shadows make it obvious that beneath him there is an unseen light source.
When Geri and Mick are hurrying away in Geri's station wagon, there is a squealing sound made by the tires, but at the same time, a close-up of the tires shows they are on dirt/grass.
Near the end of the film, when Roger is attacking Mick, you can clearly see lights on in the house, even though all the power is supposed to be out.