When the house passes too close to Tsouris-3 and enters its gravity field, objects in the house and attached to the house begin to fall toward Tsouris-3 and away from the house, but all objects, including the house itself, would be subject to the same gravitational force and would fall toward Tsouris-3 together, as demonstrated by Galileo at the Leaning Tower of Pisa.
Danny asks his father to play "Smash Brothers". This is an obvious reference to a series of Nintendo games titled "Super Smash Bros." that is only available on the Gamecube and Nintendo 64. Danny is holding Sony Playstation 2 controllers.
When the astronaut sets fire to the sofa and kicks it out of the door into space, the couch shouldn't burn because there is no oxygen. Given that the characters can go outside and breathe without any harm, such a detail can to be excused.
When Danny breaks the broom on the kitchen table, you can clearly see it has been sawed halfway through.
When Danny first finds the game he looks at the game and says to Walter "what's Zathura?", clearly able to read and pronounce such an unusual word. But just seconds later after the first card pops out he struggles with the phrase "Meteor shower, take evasive action". Throughout the rest of the movie Walter needs to read the cards and Danny even tries to read another card and he is unable to read words like "rescue" and "stranded".
When Danny get a card that says "Shipmate enters cryonic sleep for 5 turns," it actually takes 8 turns.
The Games has total 51 spaces (Danny wins the game with the following spins - 5,4,7,6,6,8-2,9-1,1+9). Walter after spinning 6 times is at space 54 (9+2,8,6+4,8,8,9), which means he should have already won the game. But he continues to play and gets a 3, moves back 3 spaces to get an additional card.
When Walter is watching SportsCenter, he changes positions between the one close-up of his head and then the medium shot of him on the chair.
From the point where Danny is behind the wall listening to Walter complain to his father about the fact that he works too much to the point where Danny knocks over the fruit punch that spills over his father's picture, his hair is sometimes parted and sometimes not.
The circular saw that the defective robot grabs from the hatch in its back is shown in most shots to be held closely between the robots two fingers - except when the saw is being used to cut the fireplace; here the saw is shown to have a large hub between the blade and the holding fingers.
Josh Hutcherson's (Walter) hair changes style frequently throughout the movie, even though the film is set in one day.
When the Zorgons first appear, they shoot out the windows in the kitchen. But later, when the astronaut is telling the kids to shut off all the lights, the windows are intact.
The house uses a large boiler for steam heat, yet no steam radiators are visible in any of the rooms in the house.
When the father goes into Lisa's room to wake her up, she is seen sleeping with a bunch of white colored pillows. A shot later, there is a purple pillow next to her. A few more shots later, the pillow is gone.
When Danny is on the Zargon ship trying to avoid being seen by the Zargon, while grabbing at the game, you can clearly see the arm of either a camera man or puppeteer just to his right. He dodges back and forth and the arm is there at first then gone on the second attempt.
When the astronaut first arrives, Walter tells him he is a "fleet admiral" in an attempt to make him leave. The astronaut then responds that he is fleet admiral as well, even showing him the card which shows that he used to be a player. Later, when the astronaut is telling the boys about his failed attempt at a shooting star wish Walter exclaims "You were a player?" He should've been clued into the fact that the astronaut was indeed a former player when he showed the boys the card. However, Walter could've assumed that the astronaut was lying to them in order to stay in the house, but it wouldn't explain where his card came from.