From Harry Potter and the Goblet of Fire:

(part of the sphinx's riddle to Harry, during the third task of the Triwizard Tournament)

And finally give me the sound often heard
During the search for a hard-to-find word.

(as Harry sorts the riddle out, this is what he comes up with)

"A sound often heard in the search for a hard-to-find word," said Harry. "Er...that'd be...er...hang on - 'er'! 'Er's a sound!"

The sphinx smiled at him.

The sphinx's riddle in that Harry Potter is NOT one that a Canajun child could solve, methinks (but perhaps other Canucks here may wish to contradict me?) - because Canajuns don't say "er" when they're thinking - we really tend to say "um" or "ah" (or, as in the case of someone I knew at high school, "um-ah").

Let us go in peace to love and serve the board.