A previous partner of mine purchased me a DVD on Sheepdog training. I learned a lot, for a while even trained girls to respond to specific series of commands using a sheepdog whistle. She was very kind, and thoughtful. She saw my delight at a sheepdog display, and went out of her way to find me the best resources on it. Whistles are for people who need to to communicate complex commands across a crowded nightclub without shouting.