I'll run further with the 2D/3D analogy.
A 2D being could not ever hide from the 3D perspective - Thus a 3D being can see everything the 2D being does.
A 3D being (or whatever part interacts with the 2D world) could appear to move thru walls to any 2D being. The 3D being simply uses the extra dimension to bypass them.
A 3D being could take a 2D being completely out of the 2D beings world. Any 2D being witnessing this would see the abducted 2D being as vanishing into "thin air". The 3D being can also use this trick and completely vanish from the 2D world.
Remind you of any Biblical stories?
thanx
PM1K