<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 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()