Darcy's Leg Game

Darcy has a new game, and I'm wondering if I should schedule a preemptive vet appointment – for when she breaks her leg!

We've never been sure exactly what Duncan was doing when he broke his leg, but it was some kind of twisting or spinning movement. Possibly tail-chasing, which he quite enjoyed. Well, Darcy feels that if she's going to equal or surpass him (which seems to be her goal in most things), she might as well be a bit more direct about it: skip the tail (hers is longer than his anyway, so not really a challenge to catch) and chase the leg itself:

I'm trying to convince her that this game is not a great idea.