Gosh, OT. I remember what you are talking about. We called it a "whip chain" and had to use it on an old mare that you could not catch. After about two times, she figured out how to run with it on, though, and it never caught her leg and it never slowed her down.
What a horse! She was a good one after you caught her, but catching her was something else. When my sister-in-law was a little girl, she used to love to ride her after school, but no one could catch her. She would put oats in the trough in the corral, climb up in a tree that was near the corral and wait for the old mare to come in. Just about sundown, the mare would cautiously approach the corral, go in and eat the oats. The little girl would jump out of the tree, run like heck to get the gate shut. The old mare would always beat her out the gate. She always managed to eat all the oats as well!!
Of course, things finally changed and the mare was kept up. But she and that little girl put on quite a show for awhile.