Just tried a “monkey’s fist” knot. This is the first one I’ve tried at this size and it had six passes (ie, I wound it six times round with each change of direction) and the inner core was a polystyrene sphere a couple of inches in diameter. The tying was easy enough, although I had a few false starts using some silver-grey metallic yarn, in the hope of making a small glitterball. I eventually succeeded by switching to some thicker braided cordage we bought a few weeks ago.
With this knot, the real art is in tightening it neatly. I’m still practising that part of it, although I did recently make a rather nice smaller version of the knot, complete with a catnip ball at the core, for Smoky to play with. He seems to enjoy it and there’s little danger of his getting at the innards any time soon 🙂