This is one of those warning signs, isn't it? This is one of those times where you dismiss it as cute, or bizarre, but at the crime scene, everyone will be audibly wondering who did it, but they'll know in the back of their minds who really stabbed you in the back when you weren't looking.
My cat started doing this as some sort of game. She'll hook a mouse toy onto her claw then walk upright with it to see how long she can go without dropping it.