When Gus first wakes up in the hotel after he and Hazel spend their night together, the clock on the bedside table says 9:11. When he rolls over to read the note she left, it says 8:47.
When Isaac is destroying Gus's trophies, the pillows on the bench repeatedly appear and disappear.
When the two first meet Van Houten, he takes the last sips of his drink twice before refilling.
The taxi that brings Hazel, Augustus en Frannie to the hotel, holds during the first appearance the license plate number "4V-5RG-K" (which is not a format used in the Netherlands), but seconds later, as the taxi arrives at the hotel, the license plate is shown as "44-STR-2".
During the Night of the Broken Trophies, Isaac is holding a trophy with one column when he asks for Augustus's permission. However, in the background of the next shot, Isaac is seen smashing a two-column trophy.
Hazel Grace has had a thyroidectomy which should leave a long scar across the base of her neck, yet her neck is unmarked.
In the e-mail written by Van Houten's assistant she names May 5th as the day for the meeting. However, May 5th is Liberation Day in the Netherlands. Therefore Amsterdam would be full of festivities and people celebrating freedom and not as quiet as it was seen in the movie.
During an exacerbation of her condition, Hazel has a drain put in for her pulmonary edema. This is incorrect as pulmonary edema is not managed by the insertion of chest drains, but rather by supportive measures (chest drains are, however, used in cases of pleural effusion).
Hazel says she is going for an MRI, but you can see the tube rotating indicating that she has a CT. Then later she talks about the PET scan.
When Hazel is out of breath climbing the stairs in the Anne Frank house, she pants through her mouth. Yet to receive oxygen from her nasal canula, she would need to breathe in through her nose (something someone well-versed in using supplemental oxygen would know).
In the egging scene, when Monica's mom comes out of the house Issac throws the egg he is holding behind him and it bounces away as if it is a ball.
At approximately 1:26:45 Following the return from Amsterdam, Gus is lying across the couch, Hazel on the floor next to Gus and Gus's left leg is across Issac who is sitting on the opposite (Right) end of the couch and Gus wiggles his foot. His right leg is bent and foot is on the floor and is drumming his heel or twitching (for lack of a better description of the voluntary/involuntary movement).. An action that is only able with movement through the ankle and raising your heel in a rapid and repeated manner. Something that he would be incapable of doing with an artificial leg.
(at around 89 mins) Hazel and Gus are on an airplane. The first shot is looking out of their window where the clouds are moving by from left to right, meaning that the front of the airplane is to the left of the shot because the clouds would be moving from the front of the airplane (left) toward the rear of the airplane (right). The camera then pans left to find Hazel and Gus sitting facing to the right towards the rear of the airplane. So they are flying backwards.
When Hazel texts Gus to tell him they are going to Amsterdam, he texts her back, and when she picks up her phone it's not lit up like it should be when receiving a text.
(At 2 minutes) On the left page of the book Hazel was reading, the word "to" was written 6 times.
Arriving on the departure airport, the departures timetable is briefly shown. The flight numbers and destinations, including gate numbers, are all from flights which depart from Luxembourg Airport in Luxembourg. Most flight numbers and destinations are from Luxair, except for Amsterdam and Zurich. However, the 9723 Munich flight hasn't been flown via Saarbrucken since a couple of years, which means the shot is already a couple of years old.
When Gus, Hazel and her mother come down the escalator in the airport in Indianapolis, you see a huge poster of downtown Pittsburgh in the background.
Set in Indiana but filmed in Pittsburgh, as revealed by the distinctive PPG Tower in the skyline of a shot near the Airport scene.
Many of the cars have Indiana plates on the back, but Pennsylvania inspection stickers on the windshield.
The family car is shown several times with state inspection stickers in the window. Most of Indiana does not require any sort of safety or emissions checks, thus those stickers are not used.
When Hazel and Gus leave the hotel in Amsterdam to go to Van Houten's house, they take a streetcar to get there. However, in the email Hazel receives from Lidewij prior to the trip, it is stated that the hotel is only a street over from Van Houten's home.
When Gus narrates the letter he wrote Hazel, his voice says slightly different words than the letter contains when it is shown briefly in Hazel's hands.
When Hazel denounces Gus's tragic flaw, she pronounces the Greek word "hamartia" (ha-mar-tia) "ha-mar-sha."
Hazel says there are an infinite amount of numbers between 0 and 1 and a an even larger infinity between 0 and 2. While she was making a metaphorical point, this is wrong. These two intervals have the same infinity, i.e. the same cardinality, which is Aleph-one.