Continuity: When Jennifer finds the small boy, she removes a sheet from a mirror. In the next shot the sheet is draped back over the mirror again.
Revealing mistakes: After killing the professor, the killer gets in a car and drives away. In the next shot, it shows the killer’s point of view from inside the car as the monkey jumps onto the windshield. But you can clearly see off to the right, a large pine tree branch, and that the car really isn't moving at all.