My little void cat's favourite activity is bathtime.
I keep forgetting to take a video of it, because I like to bathe by candlelight, but before I'm even done running it, she's standing at the side, waiting.
What's she waiting for? Why, to drown her tail, of course. Only her tail. She bats it into the water like she's knocking something off the shelf, and once it starts getting soaked, she stares at it, absolutely rapt. Maybe pushes it in a little further. Then, when it's sufficiently sodden, she pulls it out, watches it drip, and then chases it around in circles being all mrrr mrp? mewl! until she can catch it and then lick it to death.
Then she hops back up to do it all again.