Step 5: Preparing the Pig
At an absolute minimum, you need a cheap, heavy chef's knife, and a standard hammer and a Bone Saw. A proper bone saw is preferred, but any hand saw would work.
Step 1 - Start at the tail end of the pig, with the pig on it's back. Using the saw, cut open the front of the pelvis and encourage (by force) the hind quarters to lay flat. You should see the back of the pelvis, and the start of the backbone.
Step 2 - Move to the head, and use the saw to cut open the breastbone; start the cut on the tail end, and cut up to the head. The rib cage should open slightly.
Step 3 - Go back to the tail, use the bone saw to start cutting the backbone near the pelvis, once you have a cut started, switch to the knife.
Place you knife horizontally along the backbone, and pound the back of the knife with the hammer a few times. The vertebrae are surprisingly soft, and the blade should cut right through. Repeat this process several times, each time cutting through 3-4 vertebrae. The pig should start to lay flat. Make sure that you don't cut beyond the vertebrae - it's easy to cut too far and come out the top of the pig. This will make an unsightly hole.
When you reach the back of the head, you have a choice to make. The pig will lie flatter and cook better if you cut the back of the skull in half with your saw. It's possible that this last step might be too much for some people. If so, skip it, but your pig won't cook quite as evenly.
Once the pig is butterflied, cover the interior with kosher or rock salt and your rub of choice, and place into the pig rack. I don't have a favorite rub recipe, so I just use Tony Chachere's rub, available at your supermarket. If you have a marinade injector, this is a good time to juice up the pig with your marinade of choice.
If you want to butterfly the pig the night before the roast, simply rack the pig, and fill the bottom of the roaster with ice. Unless you live somewhere really warm, that should keep it cool until the roast.