...

• Select the curve's shape node (select the curve in the outliner and press the down arrow).
• Add a RenderMan primvar named rmanNN
  • main menu > Modify
  • Add Attribute...
  • Long Name = rmanNN
  • data Type = Vector
• Change rmanNN in the curve shape node to anything but 0, for example, 2701, 10, 3600.
• This will supply the curve with a normal and twist the curve.

...