I had a college student who'd come in for some doggie therapy ask if she could call my dog. Since we were alone in an enclosed space, she and the dog knew each other, and I was confident about everyone handling the situation, I dropped the leash and told her to call him. He raced over to her delightedly and while he was receiving the petting he knew he'd get for responding to her call, she looked at me and said, "There's nothing better than watching a happy dog racing toward you."
Gotta admit that watching a dog rush delightedly to you, as if he can't wait one extra second to be in your presence, is pretty great.
