Freakonomics

When it comes to extras, all the stops have been pulled out, although you rather wish they hadn't been, at least in the case of the producers' commentary which has the dubious honour of being the dullest one I have ever had the misfortune to sit through. Chris Romano, Dan O'Meara and Chad Troutwine - who it's a huge struggle to distinguish between - spend massive chunks of the film sitting in stony silence, only occasionally offering pointless observations such as "great footage", "this is so good", "really interesting".

"I see the challenges in doing these commentaries," one of them says, "we have to talk over films." Shame they just didn't save themselves the effort.

Thank goodness then, for the second commentary track, which features all of the directors involved - Seth Gordon, Morgan Spurlock, Eugene Jarecki, Heidi Ewing, Rachel Grady, Alex Gibney and A Roshanda By Any Other Name scribe Jeremy Chilnick. All the filmmakers are engaging and informative, each narrating their relevant segment, and the commentary track frequently allows them to flesh out ideas and concepts from their films that suffer from the short runtime.

All of them talk about the shooting of the films and the interaction between them, the book and one another. It's interesting to hear about some of the difficulties faced, too, such as the problems Spurlock had getting access to archive footage and the challenges presented to Gibney as he tried to find sumo footage secure in the knowledge that the community itself would certainly not help him.

The additional interviews with Steven Levitt and Stephen Dubner are also well worth a look, as they detail many of their underlying concepts and attitudes when tackling a subject. All in all a good set of extras that helps fill in many of the gaps left by the films themselves.