At 18 mins 14secs of the Character Animator Complete Animation Workflow video Dave Werner drags the mouth layer from a Photoshop puppet over to the puppet he is creating. When I try to drag the mouth layer of a functioning puppet I have already created in Illustrator over to a puppet I am assembling a black "no entry" symbol appears next to my cursor and no transfer of mouth takes place. If someone can shed light on this I would be very grateful.
It looks like in the video he's dragging and dropping a group from one open Photoshop document into another one. I'm not an Illustrator expert (if somebody on the forums is, feel free to jump in with tips here), but I was not able to do drag and drop a group from one Illustrator document to another. I was, however, able to copy and paste a group from one document to another, so that might be a way to achieve the same result.