Goofs

During the last basement scene, the writing on the bottom left side of the whiteboard changes between shots, particularly when filmed from behind Regan.

The impression of her bloody footprints do not match the shape of her bleeding feet.

In the grocery store when Lee removes the batteries from the toy space shuttle, he sets them down, apart from each other. Yet when Beau goes to pick them up, they are arranged next to each other.

The Ford truck that Marcus is pretending to drive is shown with a lever-style parking brake on the transmission tunnel. Old-Body Style (OBS) Ford trucks use a pedal-style parking brake located at the left kick panel that is released with a pull handle above it.

The oxygen they are using to keep the baby quiet would blind the baby. Putting a baby in a dark enclosure like the box would trigger that baby every time, no infant would be content with that. Also, there is no realistic way that the mask would keep the baby's cries silent to the aliens since their hearing is so sensitive.

Can they use open flame next to oxygen? There would be a problem with that, like an explosion.

The family seems to have a plentiful, uninterrupted electricity supply, despite the desolation caused by the creatures worldwide. Their electricity comes from solar panels that can be seen on the roof of their house.

The monsters are depicted as having passive sonar sensing only. It means, they cannot detect you and you are safe as long as you are not emitting any sound, even though you move around the room.

However, the movie also shows that the monsters can do complex movement such as go down stairs and or go up stairs. To complete this kind of complex movement, the monsters need to know the exact positions of surrounding solid body, in this case the exact positions of each stair. And to detect the exact position of surrounding solid body, the monsters must have active sonar sensing. That is why in the movie you don't see them bumping into any walls when moving. And if they have active sonar sensing, you are dead if you move around the room while they are present.

However, it's unknown what the creatures' level of intelligence is, and they may just be exhibiting hunting behavior. While they do have some method of sensing their environment, they use sound to help them find signs of life and they wouldn't want to waste energy with something that might be part of the environment.

Lee takes his son to the waterfall to note that loud natural sounds can mask their noises, with both yelling to demonstrate. If Evelyn was so far along in her pregnancy he should have set up some kind of camp there so that any screams from the childbirth could be masked. However, it's not very practical - or safe - for the family to be living outdoors day and night in this situation.

A normal indoor conversation at a volume of 66dB would have a noise level of only 39dB at even 20m distance, close to the normal environmental sound level of a forest (~40dB). With massive dampening from walls and soil in the line of sound travel would mean that any conversation would either be inaudible or at least masked by environmental noise levels. However, as seen in the film, the creatures have actually come right up to the house on occasion. The house is not made of bricks and the family obviously were being cautious in case one of them was right outside. Psychologically, it would make sense that a family in this unique and extremely traumatic situation would probably be overly cautious.

A person deaf from birth would not know how loud a sound various actions would make, so likely could not deliberately live quietly. However, a deaf person with hearing aids or cochlear implants can make connections between collisions, vibrations etc. as making sounds. In addition to this, Regan would have been trained by her family to be very vigilant about potential noise-causing actions, as seen in her hearing brother's intense anxiety regarding making noise. It is also possible Regan was born hearing and became deaf later in life.

The corn plants in the fields are green at day 472. This means they were planted in the current season. They have a full silo of corn, so there is no reason they would have needed to plant an entire field of corn to feed their small family. Also the perfectly aligned rows imply that they were planted by machine, which would have been extremely loud.

When the kids are in the corn silo, holding onto the silo door that fell in, one side of the door is unpainted, and is revealed to actually be a piece of white styrofoam.

Taking blood pressure measurements during pregnancy is very important and its inclusion in the film was a good detail. However, when Evelyn is taking her blood pressure, the blood pressure cuff is too low on her arm and she is not using the stethoscope to record the pressure. Given that using the stethoscope greatly improves the accuracy and makes taking the measurement easier, there was no reason that she should not have used the stethoscope.

The opening scene takes place on "Day 89", while the remainder of the film occurs on or after "Day 472", or one year and 18 days later. But days 472 and beyond clearly occur earlier in the fall than day 89. As is noted in the "Trivia" section, the opening scene was filmed last because it required John Krasinski to shave off much of his beard, so it was indeed shot later in the fall. This anachronism could have been corrected by changing "Day 472" to, say, "Day 442".

In the fireworks scene, the (first) fireworks are supposed to be high in the sky above a cornfield, and the camera shot is from ground level (looking up). But you can see that the filmmakers simply superimposed fireworks over the cornfield, as the streamers are clearly in front of the corn plants.

At the beginning, when the family has left the store save for the small child, the head of a man can be seen in the window at the left of the door, the man appears to realize he is filmed and steps back, but then he is seen again.

The bulk of the film takes place over a year after the creatures arrive. That means any crops on the farm were planted by the Abbott family. But there is no way a single family, without the use of machines or animals (horses, mules, and all other farm animals presumably being killed by the creatures since they wouldn't know to keep quiet), could plant as many acres as seen in the film. The old saying in the years before farm machinery was "40 acres and a mule" for a family farm, and the Abbotts wouldn't even have the mule to help pull the plow.

At most the family could plant only a few acres. Nor would they have as many acres in corn as seen in the film since it would be too much for the family to consume. Instead they would have a wider variety of crops on much smaller acreage to vary their diet and get other nutrients.

The creatures must (coincidentally) have an identical audible range to that of humans (~20 Hz to 20 kHz) otherwise someone would have worked out that they could be easily be thwarted by broadcasting high amplitude white noise above and below these frequencies to drown out sounds of normal human activity (e.g. speech). Thus humans would be unaffected and could go about their daily lives pretty much as normal (and the creatures would eventually starve to death).

When Evelyn wakes up in the safe room with water flooding it and a creature in the opposite corner, not only is the lid inexplicably removed from the infant's safe box, but the oxygen mask is also no longer in use. If she was asleep and Lee left them there, the rising water would not have removed the lid and neither would the creature. Unless we are supposed to believe that since Lee felt it was safe enough to talk in this room and not be heard by the creatures that it was worth the risk of tempting fate by letting the baby openly cry, too, and not bother with the safe box they had assembled to guarantee its safety after all?

Lee takes his son to the waterfall to note that loud natural sounds can mask their noises, and to have some father-son time. If Evelyn was so far along in her pregnancy this might not be the right time for such excursions as she could use all the help from her family when giving birth.

When the kids are in the corn silo they make enough noise to wake the dead. The silo would have amplified this. Aliens would have come for miles.

Tokyo is misspelled on the radio checklist being crossed out in red.

While Evelyn is homeschooling her son Marcus, written on a whiteboard at the back is the first quatrain from William Shakespeare's Sonnet 18, complete with accent marks for reading the verse aloud. Since the family does not dare to speak in the house, they could not have read the verse aloud.