(at around 27 mins) When Mrs. Olson tells Casey and Stan that Mrs. Brummel has cancer regarding her dissolving body in the previous scene, a good portion of the boom mic is quite visible at the top of the screen before zooming in on their faces.
(at around 1h 3 mins) Zeke states that Scat, a diuretic, dries out the aliens. A diuretic makes you urinate and must be ingested to work and would not dry out an object on contact. Scat is a desiccant which would dry out an object on contact.
(at around 11 mins) When Zeke is in the bathroom in the beginning when he is introduced, he gives two boys free "scat", he hands it to them and both pens are facing the same way, but when his name appears, one is facing one way and the other is facing another.
(at around 1h 24 mins) When Zeke and Miss Burke are in the car near the end of the film we see Zeke putting on his seatbelt. Then we see Zeke's hands on the steering wheel. In the next shot he is still doing his seatbelt up.
(at around 1h 2 mins) After infecting a lab mouse with the creature, Zeke dissects the mouse, then removes the creature and examines it on a microscope with a scalpel still in his hand. In the next shot, he is shown retrieving the scalpel from the dissection tool kit.
(at around 17 mins) When Stokely, Delilah, and Mary Beth are outside, Delilah is talking to Mary Beth about Stokely being a lesbian. Stokely then starts putting things into her backpack. From a wide shot we seeing Stokely zipping up her backpack and nothing else is left on the table. The next shot shows Stokely grabbing her cigarettes from off the table.
(at around 1h 13 mins) During the big football game they show people holding up letters that spell "Kill" the second line of people have the second "L" upside down but in the next scene it's corrected.
(at around 12 mins) In the faculty lounge near the beginning of the film, when Mr. Tate has the line "Can we say retirement?," Mr. Furlong's green jacket can be seen next to him. However, at that point, Mr. Furlong is actually talking to Nurse Harper and her patient by the table. Furlong doesn't move next to Tate until later in the scene.
(at around 58 mins) When the gang is walking out of the school heading towards Zeke's car, you see a girl in a green shirt walking by, and then, in another shot, standing up on the park bench staring at them.
(at around 21 mins) When Casey shows Mr. Furlong the new species, Casey always has his backpack slung across his chest, but towards the beginning of the discussion of the new species, Casey doesn't have anything slung across his chest. The next shot of him and future shots all have him with the backpack slung across his chest.
(at around 30 mins) When Casey and Delilah are in the faculty lounge and Casey sees the shadows behind the door, he drops his camera on the table and him and Delilah run into the closet. Later on in the scene, the camera is no longer on the table, and nobody has grabbed it.
(at around 31 mins) When Coach Willis and Mrs. Olsen enter the faculty lounge, they walk to the water cooler. Mrs. Olsen splashes water on her face and getting some of her hair wet. In the next shot, her hair is dry and perfectly brushed.
(at around 1h 26 mins) Marybeth asks Stokely how the book Invasion of the Body Snatchers end, Stokely replies, "They get us. They win. We lose." But actually the book ends with the aliens giving up because they had underestimated the human desire for survival.
(at around 1h 7 mins) When Zeke hands out the Scat pens to determine who amongst them may be an alien the blue cap is still on as they inhale from the other end. Now unless they have a huge inhaling capacity there's no way to inhale a whole pen's worth with one end of a tube sealed.
(at around 48 mins) Zeke tells Miss Burke "It's too Hot", yet he's seen clearly wearing a waffle shirt under his dark t-shirt. Waffle shirts are made primarily to keep one warm, so why would he be wearing one under his t-shirt if it's "too hot"?
The goof items below may give away important plot points.
(at around 1h 30 mins) While Marybeth is walking naked through the locker room and her shadow shows her tentacles, we hear her talking. In the shots from behind and from the sides her mouth is not moving.
(at around 1h 9 mins) When Zeke hands Marybeth the pen of scat, he removes the blue cap from it as he hands it to her. Marybeth is seen spinning the pen, which we later learn is her emptying it. The shot switches to Delilah about to snort it, then back to Marybeth who now has the cap on her pen.