Great acting is what elevates a film from your everyday run-of-the-mill popcorn flick to a timeless classic. Sometimes, it seems as if the reactions we’re seeing on screen are just too genuine to be anything but.
As it turns out, more often than not, that’s actually what transpires. It’s up to camera crews and directors to be able to capture those precise moments when actors actually aren’t acting at all.
Alan Rickman really was dropped in *Die Hard*.

The director had told Rickman that he would be dropped on the count of three. In order to illicit a true fear response, Alan was dropped early on the count of two.
The cast didn’t know that Geoffrey Rush would be returning for *Pirates Of The Caribbean: Dead Man’s Chest*.

The rumor around the set was that Zoe Saldana was the one who’d be making a climactic cameo. The looks of surprise on the faces of Orlando Bloom and Keira Knightley are therefore incredibly real.
Sigourney Weaver and the rest of the cast wasn’t sure what would happen during the chest-bursting scene in *Alien*.

If you haven’t seen alien , the chest-bursting scene is one of the most iconic horror moments of all time. The best part is that none of the actors saw it coming and one person even fainted!
Josh Brolin ruined the big pirate ship reveal in *The Goonies*.

Absolutely none of the actors, the kids nor the adults, had seen One-Eyed Willy’s pirate ship prior to filming the scene. Apparently, Josh was so taken aback that he exclaimed “Holy [expletive],” and the scene had to be reshot.
That’s real gunfire in *Boz N The Hood*.
Film star and hip-hop legend Ice Cube confirmed that not only did the director not tell the actors that a gun would be fired off at that moment — but he also wasn’t firing blanks.
Will Ferrell didn’t know when the Jack-in-the-Box would go off in *Elf*.

Director Jon Favreau was actually the one controlling when Jack would pop out via remote control. The fear and apprehension we see in Ferrell’s face is the real deal.
Harrison Ford’s anger and frustration during the interrogation scene in *The Fugitive* was 100% genuine.

The director wanted Ford’s reactions to the questions to be as realistic as possible. Not only did Harrison not know which questions would be asked, but his responses were also ad-libbed.
Dustin Hoffman and Katharine Ross didn’t know when the director was going to cut in *The Graduate*.

There was also nothing in the scene or script that indicated to the actors that they should gradually change their facial expressions. It was just the natural reaction of their energy fleeing the scene.
None of the children had any idea what the Chocolate Factor would look like in *Willy Wonka And The Chocolate Factory*.
Director Mel Sturt wanted to ensure that none of the young actors were able to sneak a peek at the elaborate sets until they were complete. He wanted to capture their authentic awe and surprise on camera.
Allen Danziger’s scream in *The Texas Chainsaw Massacre* was ad-libbed.

Director Tobe Hooper kept Leatherface’s costume and mask a secret from the cast. Allen Danziger’s scream when he first sees the terrifying killer wasn’t in the script at all.
Absolutely no one knew there was a body underneath the table in *The Rocky Horror Picture Show*.

When you see the actors recoil in horror, that’s because they’re legitimately terrified. Tim Curry was the only person in on the gag, and only because it was him who pulled off the table cloth.
Leonardo DiCaprio’s reaction to his bloody hand in *Django Unchained* is sickenenly real.

When Leo slams his hand down atop the turtle shell table, he really does slice his palm open. You can literally watch his hand get bloodier and bloodier throughout the scene.
Those are Kevin Heffernan’s real parents in *Super Troopers*.
In one of the most hilarious and iconic moments of the film, Rod Farva (Kevin) pulls over an elderly couple and proceeds to call the man a “chicken [expletive].” Neither his father nor mother had any idea what their son was about to say, let alone curse.
The Roman sentries in *Life Of Brian* weren’t supposed to laugh.
During the fake name scene, when the Roman soldier says the name “Biggus Dickus,” muffled laughter can be heard off-camera. The other soldiers in the scene were under strict instruction not to laugh but couldn’t hold back.
Drew Barrymore was genuinely terrified talking to Ghostface in *Scream*.
This is because none of the young actors on set were allowed to meet the actor playing Ghostface. The telephone call between him and Drew at the beginning of the film happens in real-time.
h/t: Reddit