Foley

Foley effects are sound effects added to the film during post production (after the shooting stops). They include sounds such as footsteps, clothes rustling, crockery clinking, paper folding, doors opening and slamming, punches hitting, glass breaking, etc. etc. In other words, many of the sounds that the sound recordists on set did their best to avoid recording during the shoot.
The boom operator's job is to clearly record the dialogue, and only the dialogue. At first glance it may seem odd that we add back to the soundtrack the very sounds the sound recordists tried to exclude. But the key word here is control. By excluding these sounds during filming and adding them in post, we have complete control over the timing, quality, and relative volume of the sound effects.
For example, an introductory shot of a biker wearing a leather jacket might be enhanced if we hear his jacket creak as he enters the shot - but do we really want to hear it every time he moves? By adding the foley sound fx in post, we can control its intensity, and fade it down once the dialogue begins. Even something as simple as boots on gravel can interfere with our comprehension of the dialogue if it is recorded too loudly. Far better for the actor to wear sneakers or socks (assuming their feet are off screen!) and for the boot-crunching to be added during Foley.

How is Foley Done?

Foley is usually performed by Foley artists. Ideally they stand on a Foley stage (an area with a variety of possible surfaces and props) in a Foley studio (a specialized sound studio), though any post production sound studio will do with a little modification. The Foley artists can clearly see a screen which displays the footage they are to add sound fx to, and they perform their sound effects while watching this screen for timing. The actions they perform can include walking, running, jostling each other, rubbing their clothing, handling props, and breaking objects, all while closely observing the screen to