The cigarette smoked by Sigourney Weaver in Avatar is completely CGI.
O.J. Simpson was considered for the lead in "The Terminator".
Like Facebook, Star Wars was originally prefixed by the definite article ‘The’. Much cleaner without it.
While filming Rocky IV, Dolph Lundgren punched Sylvester Stallone's chest so hard, his heart slammed against his breastbone, causing it to swell and his systolic blood pressure shot to over 200. Filming was halted as Stallone was flown to a nearby hospital and spent eight days in intensive care.