Amy is seen walking through a heavy snowstorm, but by the next morning, the several inches of snow have disappeared and the trees are green.
Reese's hair style and color changes several times during the car scene, with Amy.
When Lisa sits up in the bathtub, looks over and sees her killer, there are things scattered on the floor of the hallway. When she slips and runs to shut the door the floor is clean.
When Stan is attacked in the terror train ride, the miner's light on his head is knocked off. When the shot next cuts to him it is back on his head, then off, then back on again.
Sandra takes longer turning around to see the killer holding the video camera than she does when the footage of her murder is screened to the crew in the next scene.
After Lisa wakes up in the bathtub to see her kidney removed, she hastily calls the police on her phone who promptly hang up after she tells them that she woke up in a tub of ice with her kidney gone. In real life, 911 operators are supposed to take all emergency calls very seriously no matter what so even if her emergency is reminiscent of an Urban Legend, they would never hang up on her.
The kidney they use is a bovine kidney. A human kidney does not have external lobes like those you can see on the one shown in the movie.
When Sandra forgets her keys she tries to open the car door and does not set off the alarm. She kicks it and the car alarm goes off. That's the way that particular alarm works.
When Professor Solomon hits Trevor the first time with the shovel, it is solid. But, when he prepares to hit him the second time, it appears to move as if it were rubber.
When Amy and Vanessa are hiding in the tower closet Vanessa says she doesn't hear anything. Her lips say something else.
When Amy is chased down to the lake outside the college, a crew member is clearly visible (wearing a puffy blue vest and jeans) trying to step behind the boat dock shed as the killer walks onto the dock.
The cameraman is reflected in the window of Professor Solomon's office.
When Reese drives Amy to the library, she mentions the story of a serial killer killing 8 students (in reference to the first movie). Not only was the body count listed incorrectly, in that film, only 6 students were actually murdered. Michelle, Damon, Tosh, Parker, Sasha, and an extra in the radio station. The other 4 deaths were Principal Wexler, the Dean, the Janitor, and supposedly Brenda who we find out at the end actually survived. 9 total deaths.