Revealing mistake: When the camera shows the coffee cup in the cop's car, you can see the ignition is in the off position. (00:09:16)
Revealing mistake: When the coffee cup tips over onto Officer Burke's lap, you can see the device that was making it vibrate. (00:10:04)
Revealing mistake: When Evan slips and falls on his back, you can see the 'ground' vibrates right when Evan's body hits it. With that amount of impact, a concrete ground wouldn't visibly vibrate like that. Of course the filmmaker wouldn't let the actor fall on something concrete for safety. (00:25:55)
Revealing mistake: When Nora's son gets killed, we can see the boy under the falling piece of glass. But in the shot where this piece is just about to smash him, you can see on the DVD edition that there is a dummy instead of him because his arms are too long relatively to the whole body and also the hands are obviously not human. (00:41:20)
Revealing mistake: When Tim runs into the pigeons and the glass falls: when it crushes him, you can see the arm bend backwards, same with his hand. When he gets snapped in half, the blood is water with some red food coloring stuff, not real blood. It is obvious that Tim is a rubber dummy. (00:43:09)
Revealing mistake: When the officer is looking at the pictures of the Flight 180 survivors and their deaths afterward, notice that Todd is shown still struggling at the ropes and looking into the camera. Apparently the media thought it would be better to take a picture of Todd as he was committing "suicide". A similar incident occurs with the bus accident picture. The girl is obviously splattered in the first movie, but appears to have mostly leg damage in the pics.
Revealing mistake: After the logs fall off of the trailer at the start you can see the truck jackknife and behind you just see a car flip on its side and exploding without any obstacles near it.
Revealing mistake: During the beginning crash sequence, you can see the tubes that fire a log in order to flip the cars. When the Mustang flips, you can see the flame from the charge in the tube. The red SUV has a visible flip tube as well.
Revealing mistake: When Rory gets cut in half by the fence in the wide shot(if you look closely)you can see the outline of the green suit he is wearing.
Revealing mistake: At the beginning of the movie, (outside Kimberly's house when she says, "We're gonna go meet the guys") one of the extras in the background (he is clipping the hedges) keeps looking at the camera. [This was pointed out on the DVD].
Revealing mistake: When they are all in the van to meet the pregnant woman, tyre marks from the camera car are visible.
Revealing mistake: In the pile-up scene when Kim's car starts to flip, you can see that the driver side window is removed and placed with plastic wrap, probably to protect the driver. This is on the DVD.
Revealing mistake: At the beginning of the film, even though the sky is cloudless and clear blue, the streets and highways are uniformly wet, as if a storm had just swept the area. Then, even though all of the vehicles on the highway are raising clouds of wet spray, none of the vehicle windshields are splattered with moisture, and none of the vehicles are using their windshield wipers. In fact, the only time we see a woman use her windshield wipers is when the guy throws a lit blunt onto the woman's windshield and it catches some dry leaves there on fire. So, in summation, dry leaves catch fire on the windshield of a car in spite of heavy road spray on a wet highway on a cloudless day. Multiple inconsistencies.
Revealing mistake: When Rory gets sliced by poles, if you look close the poles can be seen hitting an invisible pole then bounce on the ground.
Revealing mistake: When Kimberly's car gets flipped around a bunch of times, the dummie's limbs flopping around are quite obvious.
Revealing mistake: When Kim's in the car explaining her premonition, she turns on the radio and the time is 8:24. When Officer Burke approaches the car, it's only a few minutes later. But later when Officer Burke, Kim, and Clear are checking the tape to identify Isabella's license plate, the time on the tape says 9:12.
Revealing mistake: Widescreen. When Rory gets sliced in thirds, the bottom of his legs are not visible: the grass cuts through his legs. Post Production forgot about John Cherry's legs.
Chosen answer: Eugene's death had no clues I know of, but Clear and Rory's did, Rory's clue was with Nora's. The trophy's shadow is segmented, giving it a divided look, Rory ends up divided to pieces by the barbed fence. As for Clear, Bludworth hints at it with his comment "such fire you have now".