(It may be argued here that the Bene Gesserit sent their Missionaria Protectiva onto Arrakis centuries earlier to implant something like this legend as safeguard should any members of the school be trapped there and require sanctuary, and that this legend of "the voice from the outer world" was properly to be ignored because it appeared to be the standard Bene Gesserit ruse.
There are no more uses of "ruse" in the book.
Show samples from other sources
She pretended to need help with her homework as a ruse to see him again.
She knew her opponent too well to fall for that ruse.