Patching is done in the Boolooroo's royal palace, in the Room of the Great Knife. The room is high and big, with rows of benches for spectators and a raised platform for the royal family. The great knife is like a guillotine, built into a huge framework like a derrick that reaches to the ceiling. The immense blade is so heavy that it takes the strength of seven Blueskins to raise it, and the Boolooroo himself pulls the cord that releases the blade. Set below the blade is another framework set on rollers to which prisoners are tied to keep them from wriggling and to make sure the slicing is accurate.
Using the giant guillotine, two victims are sliced in half. Since the Blueskins cannot die until they have lived a full six hundred years it does not kill them, but it is very unpleasant. Each half person is patched to the opposite half of the other person, creating two new mismatched people. It destroys individuality and makes those patched into complex creatures who refer to themselves in the plural.
No one who has been patched can ever be Boolooroo. It is also against the law for a patched person to marry; it's regarded as half-bigamy.