The Kûd-dûkan is a creature in Rohirric folklore. There is only one tale about them, namely that they do not appear in any other tales. They do little, and avoid the sight of men, being able to vanish in a twinkling; and they can change their voices to resemble the piping of birds. They are, however, not known to spout smoke from their mouths.
When Théoden met Peregrin Took and Meriadoc Brandybuck standing guard at Isengard on March 5th, T.A. 3019, he immediately connected them to the folklore creature. He was corrected by Peregrin, who said that they preferred the term kuduk, or "Hobbit".
It is translated into Old English as Holbytla, "hole-dweller".