Place the live mud crab in the freezer for one hour thus causing its demise. Scrub the beast with a brush under cold running water to remove any mud that may still be clinging to it. Cut the crab in half with a large kitchen knife. Reserve the juices that will flow from it together with the mustard and roe, if there happens to be any. Remove the top โshieldโ of the crab and discard together with the feathery gills around the top of the legs. Sever the legs and claws with a kitchen knife or sharp cleaver. Crack the claws with sharp blows from the back of the knife or cleaver. Cook immediately. Crab tends to lose its moisture if there is any delay.