Continuity mistake: As Gerry, Segen, and the head of W.H.O. Are walking through the cafeteria of B-Wing, the head of W.H.O. accidentally kicks a can of Mountain Dew which slides across the floor. Just after this, the other W.H.O. Scientists are shown looking at the three in 3 different security monitors. The movements of the three in each monitor is different and does not match up if you look closely. (01:29:30)
Plot hole: The same zombie who can smell through a vault that Gerry is not worth a bite, just minutes before couldn't smell the presence of three alive humans two meters apart.
Continuity mistake: Gerry is standing by his stove where he is cooking pancakes, looking to his right at the TV. Above the TV is a cabinet with a purple sticker on it. As his daughters and wife get up to leave the room, he is suddenly standing next to this cabinet. Then, only a split second later, as he says "Hey! Plates in the sink!" he is suddenly back in front of his stove, which is a few feet away. He moves to these spots instantaneously. (00:04:55)
Factual error: When Gerry is in Camp Humphreys, the leader of the group there tells him to make sure Maverick keeps the nose of the plane pointed towards the sun. However, since they're going to Jerusalem, and it's night time, they would likely be headed West, therefore not towards the sun but rather in the opposite direction. (00:48:40)
Continuity mistake: In the scene where the plane decompresses, the pilots are shown putting on air masks. Seconds later just before the plane crashes, the pilot is again shown, this time without an air mask.
Audio problem: While Gerry is talking to the C.I.A. Agent, a side view of the agent's face is seen as he says "That's the man in Jerusalem you want to see." The movements of his mouth and cheek does not appear to match up to what he is saying at all. (00:43:55)
Continuity mistake: The girls are kicked off the USS Argus when the military thinks Gerry is dead. Thierry sends them off on a helicopter. As they board the helicopter, we see a bridge structure behind Thierry, who is looking down the length of the ship at them - and also behind them is 'the same' bridge structure. It has been shown, in several shots through the film, that the Argus has just one such structure. (01:25:20)
Factual error: When flying from Korea to Israel, a nuclear explosion happens in the distance, the plane is hit by a shockwave, and then the phones go dead. The EMP from the nuke would have taken out all electronics first, not last. And they certainly wouldn't work again, especially a sat phone designed to receive radio waves. It would have probably also taken down the plane.
Other mistake: Despite the number of staff and zombies (former staff) at the W.H.O Research Centre, the car park leading up to the main entrance is empty but for one car.
Continuity mistake: The first guy that Gerry watches turn into a zombie, and figures out the transformation takes about 12 seconds, he sees go to his car first. The guy opens his door and his right arm is down towards the center of the door. The angle changes and suddenly his right arm is up towards the top of the door. (00:09:05)
Continuity mistake: Lane is listening to the virologist on their flight to South Korea. Sunlight alternately appears and disappears from his torso. (00:37:00)
Continuity mistake: In the car, before the first zombie attack seen in the film, the family's two daughters are in the back seat as they are playing a family game. The youngest one, Connie, leans over to whisper in Rachel's ear, and it is a profile shot of her face and arm, her neck and some of her chest visible. It cuts to a different angle as she is sitting up, and suddenly she has what appears to be a large stuffed bunny or mouse in her arms, with its ears covering a lot of her face that was not visible in the previous shot. (00:05:10)
Continuity mistake: When Brad Pitt and his wife say goodbye, her right arm is extended, but a frame later it's bent and holding Pitt's hand. (00:32:25)
Revealing mistake: During the first major panic scene downtown, as the family get into the RV, one of the shots shows a man in a blue hoodie being 'changed' by the virus. He writhes on the ground in front of a taxi - the lettering on the door of the taxi is backwards, showing it's a reversed shot. (00:10:45)
Continuity mistake: When the movie starts with the family lying on the bed, Brad Pitt's arms keep changing positions between frames. (00:03:30)
Continuity mistake: After the Mexican family lets Gerry and his family into their apartment, they sit down on the couch. As Gerry leans over and kisses Rachel's head, Karin's hand is over Connie's left shoulder. The angle changes and suddenly Karin's hand vanishes. (00:17:30)
Continuity mistake: In the scene after the plane crash, Brad Pitt is hanging by the waist with his face towards the ground and blood dripping from it. When he looks up, there are blood trails running down his face rather than towards the front of it. The blood trail should be going from the cuts toward the front of his face, not towards his chin. (01:20:45)
Continuity mistake: As Gerry is handing his daughters a plate of pancakes, he says "You mean a stuffed animal puppy? 'Cause that we can do." As he says this, the camera angle changes and suddenly one of the girl's hands can be seen up in the air together almost in a praying position. The camera cuts again and her hands are back down. (00:03:55)
Other mistake: When Brad Pitt is on the plane - I think he's landing in Israel - he doesn't take his seat belt off, but that doesn't stop him from getting out of his seat.
Continuity mistake: As Gerry enters the ship's command centre the first time, when he starts walking across the floor, we see a bearded man in the background, at the stairs against the wall, talking to someone. The camera angle changes, and he is now sorting through papers perhaps 60-70 feet from where he was just standing. (00:30:30)
Chosen answer: The significance of showing the blood drop on Gerry's tongue and him spitting it out was to back up the theory that the only way to become a zombie is to be bitten by one. After the blood touched his tongue he ran to the edge of the building and waited 12 seconds (the time it takes to become a zombie) before he stepped off the ledge. If he would have started to change he was going to attempt to jump off the roof before causing harm to his family.
Then how does the scientist at the WHO get infected from a blood sample?
You can't turn by ingesting, or getting the blood on you. It has to enter your bloodstream. The scientist cut his hand and got zombie blood into his bloodstream.
He stuck himself with an infected needle or a "sharps" tool coated with infected fluids, which cut him.
Blood tester is encased in glass. Dr. Testing did not pay attention. His hand was in the case while it was mixing. Glass broke, cut him, testing blood mixed with his.