 The opening is a fragment of a scene that was meant to occur    immediately following Tiberiuss death (this is why Caligula is    clean shaven in this scene, but has a beard in the next). It was    supposed to depict Caligula and Drusilla enjoying their new    freedom as they no longer need to worry about being seen by    Tiberiuss informers. The scene is almost certainly shorter than    it was intended to be, and thus is now a meaningless fragment.  