Just takes a lot of boredom and lots of muscle memory. Not hard, per se, but unrewarding until you've put more time into than you'd think. A lot of skills within a week or so, you should have some sort of improvement to show for it. Not so much with contact juggling.
But once you've gotten ok at it, it kinda looks like magic.
Yeah, I like the look of that much more than the previous version!