Holly- Sonix

  Holly spiraled down through the faux light, searching her helmet console for the Sonix button. Sonix were generally used on canines, but in this case it might provide a moment's distraction.
...
  Generally your average troll would be at the very least irritated by the ultra-high-frequency tone. But this particular beast didn't even shake his shaggy head. There were a couple of possibilities: one, the helmet was malfunctioning; two, this troll was deaf as the proverbial post.

  Unfortunately, Holly had no way of knowing as the tones were inaudible to fairy ears.

-Artemis Fowl, Chapter 8