Nazgul Withdrawal at Weathertop
Elinor

I have just read the debate about this. As I remember it, the ring was borne of evil intent. The Ring exerted pressure on Frodo to put on the Ring. Wearing the Ring made Frodo visible to Sauron who could then bend Frodo to Sauron's will. Frodo would become as a Nazgul, neither living nor dead, but a servant to Sauron. Aragorn and Gandalf forever warned Frodo against wearing the Ring. Therefore it was not because he wore it at Weathertop that the black riders retreated; the aim was to always to will Frodo to put it on.

I would say that it was brave Frodos stab at the King (didn't he catch him in the foot?) and of course the power radiating from Aragorn (but then I would say that cos he is my favourite!)and all that stuff everyone has said about them not being the full Nine and biding their time etc.