Related to fall protection training, this might be a practical demonstration of the extension length of different types of lanyards (the "rope" that secures the body harness to the anchor point) using weighted dummies. Some lanyards will stretch a few inches, some several feet. Their use varies depending on total fall height, anchor points, work space requirements, really a lot of different factors. But use the wrong one and you'll wind up with broken legs and a wedgie instead of a safety report and buying beers for your coworkers.
I doubt that's what's being demonstrated here, but it's a possibility
Edit: turtle loving duck, just to be clear, i was mansplaining for the masses. You clearly have a firm grasp of fall protection