Originary terror is the fear of the originary violence, which compels the aborted gesture of appropriation.
The unpredictability of the originary violence makes it unlike any violent situations the hominids would have faced in the past. Everyone knows everyone else wants the object, but no one knows who is going to get it and what the others and oneself will do if the drive to appropriate it continues. The spectre of this violence creates the originary terror, which causes one of the hominids to abort their appropriation of the central object, starting the mimetic deceleration and subsequently turning into the originary sign.
Originary terror is what compels us to always try and maintain linguistic presence; a complete breakdown in presence would result in the originary violence, the unpredictability of which makes it more terrifying than any other type of violence.