Reacting to body parts

Without attaching an object is there a way for a scripted object to react to body part's movement

say you move your leg or bend it the object maintains orientation and distance from the limb.

or it reacts to head movement to 'look' in the same direction as your AV

In a word, no. Animations are played client-side and so there is no way for a script to detect the actual position of a body part at a given moment, attached or not. There isn't even any guarantee that it looks the same to all observers at any given moment.

In fact we're all running around in the T pose, we just don't see it. This is why our limbs and attachments are phantom, and we are seen in-world as a simple collision box. You can see this when your connectoin is lagging to load the animations just after teleporting to a busy area.

That said, you could possibly detect the avatar is playing animation "x" and make a guess based on timing but this will only give you gray hair.