More often that not the special features found on DVD's aren't really that special. The "behind-the scenes" featurettes, for example, are usually little more than extended studio-sanctioned commercials for the movie. Characterizing them as "puff" pieces is being extremely kind to them. Sometimes a DVD extra will actually go more in-depth into the film and reveal something truly interesting, though perhaps not always flattering, about its production (Laurent Bouzerau does a good job of this I think). On rare occasions, though, a bonus feature will have little or nothing to do with the film itself but will expand upon the ideas contained within the movie in an original and intriguing way. Children of Men includes a feature called The Possibility of Hope in which director Alfonso Cuaron examines the themes of his film in a manner that only he can. It is an excellent documentary and Ted writes a good complimentary piece about it over at The Cinematic Art.
The following 7-minute clip is a rather humorous and eminently entertaining, but still thought-provoking, animated short that appears on the unlikely DVD Final Destination 3. The title is "It's All Around You" (in reference to death) and I must say that I quite liked it. Finding it recently was like unearthing a precious stone inside of a big dung heap.*
*I should mention that despite the varying quality of the three FINAL DESTINATION movies, I do have a lot of affection for them (particularly the first one which I find to be one of the most under-appreciated horror films of recent years), not least of all because in addition to involving the usual horror-movie subjects of good, evil and our own mortality, they also deal with frightening, but nonetheless important, concepts like pre-destination and human freedom.