1) Django Unchained (2012)
Leonardo DiCaprio, playing Calvin Candie, slams his hand on a table and cuts his palm on a glass, but instead of flinching for the camera, DiCaprio used this real injury to heighten the scene with his hand bleeding aplenty as he continued to talk for his monologue. In this scene, Kerry Washington and the rest of the cast were left in character, and so an intense and uncomfortable moment unfolded as DiCaprio spread his blood onto Washington's face.
It added such a visceral quality to what was turning out to be then the most disturbing scene prepared for this film, that eventually stood out as one of the film's most memorable scenes. This happened because Quentin Tarantino chose to keep the take since DiCaprio was thoroughly into the character.