Ya, and it would have a bit of a twist across the surfaces because it is steeked near the bottom of the fell... That would mean that the inside edge is moving a different amount... posibly even in the oppizit direction from the outside edge of the pleat.

If that is the case the flexability of the fabric in the bias direction also may play a role in this movement.

The reason I am asking is because I don't think that the same weight fabric in most other materials would swing in the same way as wool. For example, cotton twill doesn't seem to move in the same way as wool in about the same weight range. I don't think it is completely the weight that is causing this swing.