This is idea from the category “thought up in advance” and “written down in a notebook”, but as it often happens – modernized during shooting process. Initially we wanted to use hands of the assistant, hidden somehow behind the back of model.
But fortunately we asked model to try to clasp her back with right hand and to put out on the other side her left hand. We liked the result and stopped on this pose. It was necessary only to take out the left hand from a sleeve, having left it freely to dangle.