Director 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, nor learns of his fate.
(at around 53 mins) 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 film's tagline, "We've sensed it. We've seen the signs. Now...it's happening," referring to M. Night Shyamalan, who wrote and directed The Sixth Sense (1999), Signs (2002), and The Happening (2008).
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 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, Pennsylvania.
(at around 32 mins) 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.
The trivia item below may give away important plot points.
(at around 1h 23 mins) 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 shaped 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.