20 Things You Somehow Missed In Alien
10. Those Reactions
In so much as they can be, the reactions of the crew to seeing Kane's chest explode were real. Ridley Scott had deliberately kept details of that scene to himself, refused to allow any of the actors on set while the props were being set up, and had it filmed with several cameras in order to make sure it was captured on the first take.
The shock, the panic, and the revulsion seen - particularly on Yaphet Kotto who allegedly returned home traumatized after filming - are as close to the real thing as was possible. Veronica Cartwright actually credits this with producing the most authentic scream of her entire career.