Using swivels with suspension allow you to spin the bound one to face whatever direction you wish, making them extremely convenient.
But when the bound one is floating in mid-air, even the tiniest amount of strength can cause them to spin and make the rope hard to control.
When preparing and undoing rope while using a swivel, make sure that you support the bound one with your own body so that they doesn't start spinning.
It may be hard to see, but in the above image, I'm supporting her body as I prepare the suspension rope.
As you can see in the below image, if you try to undo decorative suspension rope with only one hand, it will cause the body to spin.
These are also situations in which you should use your body to support the bound one, as you undo the rope.
In the below image, when you use semenawa (rope specifically designed to further constrict) to curve the bound one backwards (in a reverse shrimp pose), bending their legs back, if you pull only one of the ropes (in this case, the right rope) constricting the legs, it will cause the body to spin.
If you balance the pressure on the rope that's being pulled, the body won't spin. (Look at my right and left hands in the below picture)
In the above picture, my right hand is pulling right, while my left hand is pulling left.
The below picture is how it looks when it's finished.