I've wondered what they used too, but I don't mind it. ...Now the sounds the queen makes just give me chills of joy. Just the sound of her breathing is so awesome. I'm more curious as to how they made that sound.
...Getting on the subject, the original sounds of not only the creatures, but the technology has always impressed me. The doors opening, the computer chirping; it's all so different from anything I've heard in any other film.