def METHOD_NAME(self):
    """Split each hexahedron into six tetrahedra."""
    t = np.hstack((
        self.t[[0, 1, 3, 4]],
        self.t[[0, 3, 2, 4]],
        self.t[[2, 3, 4, 6]],
        self.t[[3, 4, 6, 7]],
        self.t[[3, 4, 5, 7]],
        self.t[[1, 3, 4, 5]],
    ))
    return MeshTet1(self.doflocs, t)