Visible crew/equipment: There is a shot of Holly crawling through a tight space with the camera facing her moving backwards as she crawls forwards (about 30 minutes into the film). In this shot, the wheel marks of the camera can be seen on the ground in front of her. (00:30:05)
Visible crew/equipment: When the girls light the first flare in the cave, the top of a crew member's head is visible, as he is crouched behind a rock. This is confirmed by Director Neil Marshall on the DVD cast commentary.
Continuity mistake: As the gang drives towards the cave entrance, the spare wheel on the back of the car that Sarah is driving switches sides three times. (00:16:30 - 00:17:10)
Visible crew/equipment: In the shot of Holly falling and breaking her leg, a wire can be seen at the top of the frame suspending her down. (00:48:35)
Factual error: On the hike to the cave, Sarah and her friends encounter a deer carcass - a red stag, which are not found in North Carolina.
Continuity mistake: Right near the end of the film, one of the characters is driving away from the caves and eventually pulls over onto a grass verge where she breaks down in tears. Seconds later, a lorry carrying logs drives past her sounding the horn. At this point, you can see that her vehicle is now on the road.
Continuity mistake: When they are crossing the first drop, as the second girl is crossing you can see two people on the right hand side, when there should be only one.
Continuity mistake: When the girls are crossing the first chasm over the huge drop, the first two girls make it to the other end safely using a wire. When the two girls are hooking up the third girl to come across, we can see four people stood behind her. There should only be three.
Continuity mistake: When Sarah falls into the pool of blood, the torch falls behind the big rock to her left. In the next shots, the torch is on the top of the rock. (01:14:05)
Revealing mistake: Towards the end when Sarah and Juno team up to find the exit, they pass underneath some thin stalactites. As Sarah goes under them, one of them wobbles as if it is made of rubber. In reality stalactites are rigid formations and are not supposed to wobble when touched. (01:26:40)
Revealing mistake: When one of the girls falls and tries to get up to a tunnel, she grabs a large rock to help herself up. You can see the rock bend and wiggle under her weight.
Other mistake: In the hospital scene at the beginning of the film, the cardiac monitor is showing no activity, after she pulls her leads, and the monitor is featured so prominently there is still no activity.
Revealing mistake: In the blood pool when Sarah kills one of the Crawlers with an antler to the eye, she then drops it afterwards and it floats.
Continuity mistake: The license plate on the front of the car that Sarah "escapes" in at the end is on the left hand side. But in a brief shot of her driving the car over a jump, the license plate suddenly switches to the right hand side. It then returns to the left hand side. (01:32:20)
Continuity mistake: Right at the end where we see Sarah still in the cave with her daughter and her birthday cake, the number of candles on the cake changes from 5 to 6 between shots.
Answer: Love each day.