I think for the Mannequins they just copied/pasted the basic script that has been around since the Morrowind days (I remember doing a mannequin mod myself for Morrowind which also let the player change the six of the mannequin so that both armor types could be displayed - something that Skyrim still hasn't!). Basically, the mannequin is a live actor whose behavior AI is deactivated immediately once the player enters the cell so this "mannequin-NPC" stays frozen in place. Small movements are possible and likely to occur.
PS: anybody tried to see if mannequins can report crimes? LOL!

So, the mannequins are like the toys from Toy Story?
Creepy things happen behind Skyrim.
Entered in my house yesterday and found a place was torn apart like a tornado has past there.
And a whiterun folk moving out.
Those bastards, bet they enter in your house and do a "pit boy party" to have fun with us.