M. Night Shyamalan's first film in which he does not physically appear for a cameo. He is the voice of 'Joey', who calls Alma a few times throughout the movie. The audience never sees him or learns of his fate.
The bee disappearance Elliot refers to early in the movie is a real problem that threatens worldwide food production, because honeybees pollinate many fruits and crops. The problem is now referred to as Colony Collapse Disorder (CCD). As of 2010, CCD has increased. Many theories have been presented, including radiation from cell phone towers, compromised immune systems, environmental changes (global warming), fungal infections, genetically engineered crops, malnutrition, parasites, pesticides, and viruses. None have been positively identified or ruled out as the primary cause(s). A combination of factors is likely involved.
At one point, Elliot talks about primordial bacteria in Australia killing off fishermen. Pyrethrins are a neurotoxin derived from Chrysanthemum plants, specifically those native to Australia. The toxin is commonly found in organic insecticides. Pyrethrins are highly toxic to bees.
The students' hypotheses about the bee disappearance include global warming and atomic, biological, or chemical contamination. The nuclear and greenhouse "plants", which symbolize those theories, literally face one another in Filbert, PA.
In a deleted scene, Elliot and Alma have a fight, then make up. This scene was intended to serve as the movie's introduction. The filmmakers removed it so the audience could learn about the couple's issues as the narrative unfolded. The scene appears on the DVD.
The exact answer to Julian's math riddle, with the average month having 30 days, is $10,737,418.23. (The answer is not $10,737,418.24, because Julian is asking about the total sum of the amounts from all days, and every amount is an even number except the amount on the first day: $0.01. Therefore the total sum must be an odd number of cents.) In addition, when the month in question has 31 days, then $10,737,418.24 would be the amount on the 31st day and the total sum after 31 days would be $21,474,836.47.
Towards the end of the movie, Alma puts something into Jess's backpack. The backpack has a picture from Avatar: The Last Airbender (2005). On the next scene, Jess boards a school bus with the number "2010" on its hood. This is an allusion to The Last Airbender (2010), which was released in 2010 and also directed by M. Night Shyamalan.
The trivia item below may give away important plot points.
Just after Alma reads the result of her pregnancy test, the camera zooms to her face. Looking closely, her left eye appears to be heart-shaped. Zooming in reveals that an overhead light is reflecting off her eye giving the heart shape appearance. If you zoom in on her other eye, it also appears to be heart-shaped right before the next scene, but you can also see the overhead light.