You can fully immerse yourself in the life and physicality of another person, take inspiration from one of the many beings occupying the animal kingdom, or just show up with a cup of coffee and a bagel, at the end of the day, none of that changes the fact that producing an honest performance usually comes down to an actor's ability to react to something truthfully in the moment.
That being said, sometimes even the finest actors working today can find it difficult to bring a truly authentic response to life in the heat of an action-packed, out-of-this-world or emotionally charged scene.
So, it's not uncommon for a director to keep vital information and key moments that are about to go down within a certain sequence from thespians in an attempt to conjure up a genuine reaction from them once the cameras are rolling.
Being thrown into the middle of a hellacious and unpredictable set-piece, having a co-star completely catch them off-guard with an invasive piece of improvisation, and getting legitimately scared senseless by an unexpected arrival are just a few of the scenarios these actors had no idea were heading their way.
10. Billy Boyd - The Fellowship Of The Ring
Despite it going on to become one of the most successful franchises in movie history and having a near $300 million budget in the end, Peter Jackson's The Lord of the Ring's trilogy still oddly possessed an independent movie spirit at heart.
And one of the finest and funniest examples of this free-spirited approach to working whilst putting these epics together comes in the shape of nobody telling Billy Boyd Gandalf's ridiculously explosive firework was legitimately going to blow during a famous early scene in The Fellowship of the Ring.
As Boyd and the rest of his Hobbit gang revealed during the DVD commentary for the flick, the actor playing Peregrin Took was under the impression that the actual explosion would be added in later via digital effects. So, when the time came to shoot the hilarious back-and-forth between himself and Dominic Monaghan, the panicked scream we hear burst out of the actor was very much genuine.
So was the urine trickling down his leg, earning himself the charming moniker of "p*ssy legs" from his co-star for his troubles.