Continuity mistake: When the cop tells Tree to drop the ax, she lets go of it and puts her hands up. However, her hands raise and lower instantly between cuts several times depending on the angle. On the angle facing her front, her hands are up by her head. But in the angle behind her, they are down by her shoulders.
Continuity mistake: The second time Tree wakes up, she does a mock "gunshot" to her forehead using her fingers. She then turns her head downwards. When the camera cuts, she instantly goes from looking down to looking to her right. (You have to look closely since only part of her head is in frame, but it's definitely noticeable).
Continuity mistake: At the beginning of the basketball game, there's someone in a red hoodie and a baby mask sitting directly next to Ryan. A few shots later, you can see over his shoulder, and there's someone else entirely next to him - a woman without a baby mask wearing an entirely different top. Then, a little later in the scene, the person in the baby mask and hoodie reappears next to Ryan in a few wide-shots.
Continuity mistake: When Ryan leads Tree and Carter to where he was killed in the beginning, as Tree walks to the closet with the baseball bat, she passes through some light and into a shadow. (There are areas of light and shadow in the room). When the camera cuts, suddenly she's back in the light.
Revealing mistake: When Tree kills herself by throwing herself out of a plane, in the shot where she lands in front of Carter and Danielle, it's very blatantly obvious she was filmed on a greenscreen and comped in. The lighting on Tree doesn't quite match the lighting of the scene, and there are very obvious and unnatural hard lines around her hair where the background was rotoscoped/keyed out.
Continuity mistake: When the group go to the DARPA HQ during the post credits scene, pay attention to the doors as they enter the lab - the doors we see on the outside do not match the doors we see on the inside, revealing the scene was shot on two separate sets. (Most noticeably, the windows on the doors get significantly narrower once they are inside the lab).
Continuity mistake: Throughout the final confrontation with Gregory, Tree has a bracelet on her left wrist. However, in the two closeup shots of her pressing the button on the magnetic medical equipment with her left hand, the bracelet disappears. (Looks like they forgot to have her wear it when they shot the closeup).
Continuity mistake: When Tree wakes up from committing suicide with the drain cleaner, she starts pouring a water bottle into her mouth. In the wide shot, her mouth is wide open, her tongue is all the way in her mouth, and there's a steady stream of water pouring off her chin. But then it punches into a closeup, and her mouth is instantly halfway closed, her tongue is pushed forward, and the stream of water has suddenly slowed to a drip. Obviously a few seconds was cut for pacing, but still a mistake.
Continuity mistake: When everyone is leaving the basketball game near the beginning, watch the crowds around the main characters as they walk down the hallway. Sometimes the extras aren't consistent from show to shot. Ex. At one point a black couple brushes past Ryan - the man is on his right and the woman is on his left. When the shot cuts to the opposite angle, suddenly the man is to Ryan's left and the woman is totally missing. This happens a few times throughout the scene.
Deliberate mistake: When Tree turns on the magnetic medical equipment, it's somehow strong enough to yank a big, heavy wheelchair up and pin Gregory in only a split-second, but not strong enough to instantly pull the screwdriver out of Tree's hand? Obviously this was done so Tree could have a cool moment where she lets go of the screwdriver and it impales Gregory... but it makes no real sense.