Boy oh boy. Where to begin?  I think Rob Zombie has a lot of potential with the films that he makes.  Hes written a decent bit, and directed that stuff and its incredibly hit or miss.  But in all honesty, I feel like he's slowly letting quality go for all of the film he puts out.  Everything after Halloween's remake is just so off the wall and strange that it doesn't gel at all.  Which brings us to 31.
31 has a very simple premise.  5 carnies are hand picked by some strangers to play in a game called 31(Which is never explained by the way.)  The goal of the game is to stay alive for 12 hours while incredibly wealthy individuals bet on who will make it out alive.  The players are stalked by whats called a "Head" who is someone that has an obsession with a specific thing defining them.  The reason that they are called what they are is honestly and truly never explained. Sex and death head show up and do absolutely nothing at all before dying.  The script for the movie plays out super easy to read.  One of these guys die, then one of these, then two of those and so on until its just one of each left, and then the movie cuts to black.  Absolutely insulting if you ask me.
Overall, the movie doesn't deserve a watch. I would only give this movie a 1/5, and would avoid it at all costs.  Unless you're watching this movie to make fun of it with all of your friends, bail out now, seriously.