Helicopter scene at the end of Mission Impossible is another amazing example of sound sweetening. It’s very similar to the Velocipod scene in The Incredibles. The scene looks great, but doesn’t really work unless it FEELS like Ethan Hunt (Tom Cruise) is about to be chewed up by the helicopter blades, that’s where sound sweetening comes into play.
Sound sweetening is about enhancing existing sounds to make them sound and feel emotionally true to the scene (enhancing is by the way the secret to cinematic storytelling).
Sound(s) used to sweeten up the helicopter blades might be sound(s) of a circular saw, but maybe it is something completely different (dental drill?). But no matter what sounds were used, they made the helicopter blades sound and FEEL really dangerous and life threatening. And that’s virtually all that matters, really.
P.S. I originally uploaded the scene to YouTube, but it is blocked in several countries (almost all English speaking). Nevertheless, you can try to watch it by clicking here.