Foley Sound

Whilst films are typically seen as very visual pieces, sound effects also play a surprisingly significant role in fully amplifying the atmosphere of even the simplest scenes, but audio from microphones used to record dialogue tend to lack overall depth and don't capture the intricacies of quieter sounds that you don't really think about, like footsteps on certain surfaces from a specific type of shoe. 

Foley is a technique used to record sound effects like these created from any objects, these are "performed" by Foley artists, who have to think creatively on how to achieve specific sounds - sometimes having to create completely made-up sounds, such as noises from fantastical creatures. 

For example, if a Foley artist were presented with a clip of a horse's hooves galloping against a field, they would have to think about how close-up the camera shot is to know how prominent the sound will be, or how heavy the horse is, how powerfully it is running, whether it is wearing a saddle that would create metallic sounds brushing against leather, etc.... and pick out objects accordingly - a smaller horse's hooves may be made using coconut shells against astroturf, whilst a larger horse might require heavy stones against dry grass.

Sometimes if a sound effect is very self explanatory and simply requires boosting, such as a door creaking open, it may also just be recorded using an actual door opening, without the need for thinking out of the box.

Here is a video showing how Foley artists record animal sounds for film, explaining the thought process behind achieving specific effects: