Freemotion couching

As far as I know this foot is only available for Berninas and then not every model.
It's so much fun to play with though finding suitable things which will fit through the hole can be difficult and then one which don't unravel make it even harder.
You can tell I'm new at this blogging business, the photos are in the reverse order I wished and not within the text. I might get better (or not).
The top photo was my very first play with the foot. The next one is a work in progress which I'm feeling in two minds about. The 3rd shows the foot and the 4th is a lovely soft knitting yarn.
It doesn't seem to matter too much what thread you use as it gets buried in the yarn.