I tried to word my question so it will be given serious consideration. Rather than ask in Pets SE (which doesn't have the brightest questions or answers), I feel it's better suited for Biology SE - specifically animal behaviour.
Generally, the play behaviour of adult cats mimic their interaction with siblings when young, and as adults, their hunting behaviour. It's in regard to play mimicking hunting that my question likely fits best.
The stealthy stalk and pounce while playing is almost identical to what's used in actual hunting but with far more playful abandon. Leaping in the air to grab an escaping bird is seen when they leap and grab at a feathered toy that's whipped about. Tossing a small fuzzy weighted toy about mimics how they act when they've caught a mouse. The same with chasing after a small rolling ball.
But there's one play behaviour I can't find an equivalent. It's cats' fascination with a simple dangling string or cord. A person doesn't even need to move it. As long as it hangs and dangles near the ground, many cats can't resist playing with it. (I'm referring to an average active cat, not one of the unfortunate inbred creatures that do little.)
Does anyone know, or can think of, an equivalent natural behaviour that explains this? It's not similar to a mother cat flicking the tip of her tail as that involves tempting movement. But it's the closest thing I can think of. I've given this a lot of thought for a long time. Hopefully, someone else has wondered too and found a reason.
(No tags really fit my question so only one given.)