its all in the picture clearly the swirl pattern represent the twisted multi dimensional nature of bon bons character allowing her to change from scene to scene every time she is shown the only onw who can see it is lyra that is why they have so much fun but bon bon is always hopping around reality as represented by the swirl only lyra knows the true bon bon because she is weird enough to look past the nature of reality and know her true form
I have learned something today. Still, Japanese didn't invent the spiral. They just made a creepy comic with spiral holes in peoples heads. Which honestly I find as one of the least attractive spirals out there. What about hypno discs? A Much preferable spiral if you ask me.
well, that's cause once you read uzumaki, you just can't look spirals with the same eyes ever again. another show with the same effect is tengen toppa gurren laggan, only that this one instead of makingyou afraid of spirals make's you think "spirals are awesome!"