Move the origin point to the cursor in Edit Mode I have a model where I would like to rotate an area of the object, in this case a mouth of a ordinary beast along a defined point, marked here with the 3D Cursor. And I am trying to move the selected areas Origin Point to the cursor, so in edit mode i press Ctrl+Shift+Alt+C and select "Origin to 3D Cursor. But then I get an error message that says, "Operation cannot be preformed in edit mode". Why??

I have Heard that you can snap the 3D Cursor to an object/vertex/edge/face but I have not found any reference of it...
It is a mirrored object btw.
What I understood  about your issue, you want to open mouth and close it. 

Please try following steps:


Select the base edges as shown in the image below, snap the 3D cursor to this edge, by hitting Shift + S and selecting Cursor to selected

Change the Pivot Point to 3D Cursor

Select the full mouth and rotate it as required.



You may also create a Shape key for easy rotate and animate

When you are done with it you may change back the Pivot point to Median point

Best of luck!