In the early years of the film's development, Shia LaBeouf dropped out of the project and the title role was briefly given to Zac Efron before LaBeouf returned to the project.
When Charlie Countryman is running back to his hostel after Gabi Ibanescu tells him she'll kiss him if he finds her tomorrow, Charlie runs without his shoes and socks on after he removed them to show Gabi a ballet move. But when he is hit by the car he has his shoes and socks back on.
During Charlie's in flight conversation with the air stewardess following Victor's death, the passengers in the rows behind Charlie are awake in one shot, asleep in the next, and continue to alternate between the two until the scene ends.