Trivia

The film-makers only used CG effects when absolutely necessary, and to enhance practical effects for the creatures rather than replace them completely. Even the smaller female alien that appears before the credits was a petite woman in a creature suit. A puppet-type head was used for some of the attack shots wherein Moses is suddenly bitten. The creature's head was a carefully constructed mask that had no eyes, and even the glowing mouthful of large, carnivorous teeth were achieved by animatronics (including twelve "servos") rather than added in post. The film-makers admit that it did help save money, but also had an unexpected benefit. The actors, rather than reacting to something that wasn't there, admitted that they were genuinely and unexpectedly frightened by the look and movements of creatures actually present (especially during chase sequences when a creature/creatures would pursue them at full speed). Nearly every actor said they felt especially intimidated-- many surprisingly so-- by the physical presence in a way they would not have if the creatures had been added digitally later. The same went for the majority of the settings; the director said it added authenticity and atmosphere to shoot on a set rather in front of a green screen. See more