Optimus Prime's Head Prop

The flickr movie pic pool has posted a all blue Optimus Prime prop. The blue is for bluescreen purposes so the CGI effects can be put over the head. What the prop itself was used for during shooting though I have no idea. Best guess is for scenes where Shia had lines where he was sitting on Optimus. Generally speaking, if the actor touches something, a real prop has to be built or the CGI would be less convincing to the eye. The pic pool is here but no idea which page for the head.

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