Look for the hinge of the shell. It should look like an exposed seam which wraps around a smooth corner. Insert the oyster knife into the seam, with the blade parallel to the seam. Use the point to do this, gently but firmly rocking the knife back and forth. Once the knife has been inserted, you can twist the blade to open the hinge a little more. Repeat this process, gradually inserting the oyster knife until you have cut the hinge completely.