Do they make a quiet, off-hand reference to a favorite obscure song? Do the filmmakers goof, misrepresenting a medical condition or use a birdsong soundtrack inappropriate for the landscape? (I wouldn't know, to be honest, but I know folks for whom this is a pet peeve.)
Here are a few details I've noticed. If you have others, send me a note through Contact the Guy, and I'll make a new list and credit you for your suggestion.
"(500) Days of Summer" -- I've mentioned before how this movie shows the characters in auto-centric LA getting around without private cars most of the time. I also like how its opening shows Summer's high school yearbook with the quote "Color my life with the chaos of trouble," a lyric from a great Belle & Sebastian album. One more thing: I missed it the first time, but the original release of the movie had a scene on the hill near the end where Joseph Gordon-Levitt calls Zooey Deschanel by Zooey, instead of by Summer, her character's name. It was fixed in the video.
"Restless" - At one point in the film, we visit the cemetery with the main characters, Enoch and Annabel. Actually, we do that a lot in this film, but in this particular scene, he takes her there to introduce her to his parents. Their grave marker, oddly, is topped with a little sculpture of two lambs. If you've spent a bit of time in old graveyards (ok, yes, I have) you'll know headstones have their own peculiar symbology. A log may suggest a life cut too short. Lambs mean innocence and are used almost entirely on children's graves. So, these two lambs are an odd movie touch on a headstone for two adults who died in recent years.
"No Strings Attached" - Another musical wink: At one point Ashton Kutcher brings a woman downstairs in his house. There's a poster for Ozomatli, the LA-based activist band known (though not widely) for great live shows. Noticed from outside the film: Mindy Kaling, who plays Shira, wrote the recent New Yorker piece about rules of chick flicks. One more little secret about this movie, though it's not something others would know. Supporting actress Greta Gerwig was in middle school with my son, but we didn't know her. We did carpool with a different girl named Greta, though. Does that count as two degrees of separation?