That's something Renoa would be interested to learn. I sort of had an idea when I read your post about the origins of her tribe. Basically my thought was that hell hounds are the servants of incubi and succubi, and such whistles are how the demons are able to control them so readily. Several generations ago her ancestors destroyed the whistle of their master and escaped hell, fleeing to earth to start a new life independent of the malicious will of their former masters. No one in her tribe today has ever been in hell, nor been in direct contact with a demon.