[dancing spawn of ungoliant]

Well, I'd suppose it has been put that way in the movie because...
Chapter 5, The White Rider: (Legolas) "We think that Sam went with him."
"Did he!" said Gandalf, and there was a gleam in his eye and a smile on his face. "Did he indeed? It is news to me, yet it does not surprise me."
I personally think that it was a nice little moment in the film between Gandalf and Aragorn.