Cats, as a general rule, don't ever pant unless they are extremely stressed out or so hot that they are basically near the point of collapsing from heat exhaustion. So, to see a cat panting and running around, obviously happy, while playing fetch is pretty weird and rare.
I got more and more annoyed with my own cat every time I see a video like this."Yes, I know you look very cute when you sleep, but I'm afraid that's not going to cut it anymore."