There is an immeasurable and untold amount of work from countless people that goes into making a movie as good as it can possibly be. Every single person who earns seeing their name in the credits at the end in some way, shape, or form contributes to what is put on the screen at the end of the day.
Like cogs in a machine, so the saying goes, though you could argue that the actors are arguably the most important cogs, as they are the ones on the screen. They are the ones who perform what everyone else prepares for them, like athletes on the field.
However, in spite of all of the work that goes into producing a movie before the actors even make it to the set, there are times when they have absolutely no idea what is about to happen. This can often be done on purpose, for numerous reasons, or it could be something more organic that happens throughout the filming process.
There have also been times that actors haven't even known when they have appeared in certain films, or were as surprised as audiences at certain scenes when they watched their performance back themselves.
10. No One Knew About The Chest Bursting Scene - Alien
The baby Xenomorph bursting through John Hurt's chest in Alien is one of the most iconic shots in the history of cinema, and Ridley Scott went to incredible lengths to make sure it looked as realistic as it possibly could.
Fear has to be one of the most difficult emotions an actor can portray, as it is so easy to see through. Real fear is far more effective, and that's what the director wanted for this scene. That's why he kept the baby alien a secret right up until it happened.
As told by Alien's art director, Roger Christian, all the actors with the exception of John Hurt were sent to their dressing rooms while the shot was set up. With the gear hidden underneath the table, though they may have suspected something was about to happen, no one was prepared for the baby alien.
There were a few different takes involved, thanks to certain technical difficulties, but even after the cast had seen the creature, Ridley Scott had another line of blood spatter added to enhance the genuine shock value. These reactions were real, and went a long way to creating such a masterful and everlasting scene.