Feigned fleeing or farciful forestalling?

[The Might]

Speculating on the second quote speaking of "some weapons that would drive back the Nine" I'd actually rather think of his voice as a possibility as well:

Such was still the power of the voice of Saruman that even the Lord of the Nazgûl did not question what it said, whether it was false or short of the full truth; but straightway he rode from the Gate and began to hunt for Gandalf in Rohan.

Perhaps some types of mind-controlling devices or something like that and not necessarily the explosives seen at Helm's Deep. Just a thought of course...