The key to this sequence was the combination of Radial Symmetry with Liquify. To replicate this, you'll need to set up a Radial Symmetry guide using the Edit Drawing Guide option in the Canvas menu. Drawing Assist for any guide, including Symmetry, can be kept active even when the visible guide is hidden. We hid the guide when shooting the video, but we've kept it active in these photos to demonstrate the process. So just create a Symmetry guide, choose the Radial option, and make sure Rotational Symmetry and Assisted Drawing are both turned on.