>>9317540They're designed with jiggle physics. the boobs, areola, and nipples each move on their own when you shake her.
I have a webm of the Rei doll being "jiggle tested" but it has sound and I'm not going through the hassle to remove the sound for a video that's NSFW at any level. But yes, the boobs do jiggle very well for being made of paper. They make a horrible squeaking sound when violently shaken though.
Here's a picture of the chest section fully opened to show the jiggle mechanisms inside.
