In modern film, almost every sound is recorded in post production. This includes even the most subtle sounds, such as clothing shifting as a character checks his wristwatch, or leather creaking as he tightens his bootstraps. These sounds are recorded behind the scenes by a "Foley" artist, who uses all sorts of materials to reproduce the on-screen movement as closely as possible.
Foley is even more important in animated movies and video games because it helps ground the impossible visuals, and brings more realism to the materials and interactions. The subtle sounds are often harder to get right than the more attention-grabbing ones because they are so unique and specific. While a stock sound library might have fist impacts and gunshots, it probably won't have sounds for "picking up a heavy object while wearing leather armor" or "stumbling on gravel but not quite falling".
For Overgrowth, I recently started working with a sound artist to start creating unique sound effects for all the in-game movements and interactions. Here is the first test of Foley sounds for movement on crete surfaces (what some of the monoliths are made of):
Be sure to check it out in HD!