    mo1 = vtkMyCallback(ren1)
    ren1.AddObserver('StartEvent', mo1)

    #
    # Now we loop over 360 degrees and render the cone each time.
    #
--
    callback = vtkMyCallback()
    boxWidget.AddObserver('InteractionEvent', callback)

    #
    # Normally the user presses the 'i' key to bring a 3D widget to life. Here
    # we will manually enable it so it appears with the cone.
