Unable to edit Proteus Puppet

Thank you both for your clarification!  I am self-taught, so sometimes I wonder if there is a simple fix that I just am unaware of.

Even after ungrouping everything under the "head" layer, I am still unable to drag a new layer underneath it.  It just gets blocked.  So I think what I will have to do is just ungroup everything, drag it out of the main +Proteus structure and under a new main +Puppet structure.  I was trying to avoid making too many changes so I didn't have to re-rig the main Proteus puppet in Character Animator, but if I need to set it all up again the practice will only help I suppose!

Thank you guys again.

This is because you're trying to drag a layer into a group. It's a little deceiving because everything is named properly (which is something you don't often see with AI files and a bunch of groups, but click on the circle next to "+nose" and hit the shortcut "Cmd/Ctrl+Shift+G"

You'll see all those paths expand because you just ungrouped the nose. You need to create a new layer then drag your nose into it, or you can click the circle icon next to "+nose" go to the Layer panel's flyout (hamburger) menu at the top-right and choose "Collect in New Layer." This will put your group inside a new layer, which you can then rename to "+nose." After that you can rename the group to something else if you want, and then put other layers above or below it.

Strange! My machine is updating all the Adobe apps for a while so I cannot check in the app at moment - just wondering if you can select head then "Create Sublayer" from the menu (top right corner of panel). I also there there are groups and layers in Illustrator, both shown in the one hierarchy. I don't think you can put a layer into a group - maybe its something like that? If so you may need to "ungroup" something, create a Layer in its place, then drag the things that were in the group into the new layer. (I never got it quite sorted out in my head to be honest, but came across the group/layer difference a few times.)