Here are a series of general training exercises for imbuing the winding jin in the various body areas:
I.e., a person has to train this stuff because "imagining spirals" has about the same effectiveness as "imagine being rich".
I'm certain a great many of us will recognize many of the motions and have actually done them as a routine part of 'normal' aikido training (or even other MA). One can go through these motions all day for years and not get it - I know 'cause I've done them and pretty sure I don't have it. There is more going on than can be seen in the vid so some one who knows how to do it has got to be there to provide commentary and direction/corrections for real progress.