More practice. All the others I took are repeatable. I heard this from afar and, having the little one in my pocket I thought "Well, Y knot try?"
It hove into view and promptly vanished behind some convenient trees. I spotted where I thought it might emerge - it did - BUT - at a sufficient rate of knotts I'd rotated about 45˚ between emergence and CLICK. And I fancied the practice; see what I started with?