My grandfather had a cat who came when he whistled. It was a short, hi-shrilled burst of sound that split all other sounds and could be heard for blocks.
We, too, were trained to come to that whistle. In fact, all the kids in the neighborhood would come running, too, because he would often hit a bucket of golf balls in the empty lot across the road and paid 10 cents for each ball gathered by us kids when he was done.
For us family members the whistle wasn't always fun and games. Often it meant "get your ass over here" - from wherever you were. It might mean a family emergency required your presence. It might mean ice cream. You never knew, but your dropped everything and hauled ass, like the cat.