Plot the point normals of a mesh.

def plot_normals(self, show_mesh=True, mag=1.0, flip=False,
                     use_every=1, **kwargs):
        """
        Plot the point normals of a mesh.
        """
        plotter = vtki.Plotter(off_screen=kwargs.pop('off_screen', False),
                               notebook=kwargs.pop('notebook', None))
        if show_mesh:
            plotter.add_mesh(self, **kwargs)

        normals = self.point_normals
        if flip:
            normals *= -1
        plotter.add_arrows(self.points[::use_every],
                           normals[::use_every], mag=mag)
        return plotter.show()