Magic in Middle-earth

[Neithan]

From FotR, Prologue, 1 Concerning Hobbits, pg 20

They possessed from the first the art of disappearing swiftly and silently, when large folk whom they do not wish to meet come blundering by; and this art they have developed until to Men it may seem magical.

Of course he may have mentioned it in the Hobbit as well, I can't remember.