Foleying

Foleying is a sounds effect technique for synchronous or live effects. They are laid manually, and not cut in to film. It amplifies sounds that would not be easily heard otherwise in original filming. Sounds are added in post-production. For example, metal tubes are filled with metal trays, empty soda cans, knives, forks, broken staple guns etc, to create sounds from comedy crashes to adding presence to something as serious as a car crash. The purpose of this is to make the quality of sound better. This video gives more examples;

SoundWorks Collection: Gary Hecker - Veteran Foley Artist from Michael Coleman on Vimeo.

Few other foleying devices used:

Wind machine: A sheet of canvas over a revolving drum of wooden slats. The fierceness of the wind is determined by the speed of the revolution. The drum is turned unevenly, for wind never blows at a constant speed. Adjusting the tension of the canvas as it's free end can also alter the sound.

Rain box: 2 wooden boxes 6'x6"x6", the floors of which are studded with nails hammered up from outside. Dried peas inside. Boxes are see-sawed to make the sound of rain.

Thunder sheet: Suspend a sheet of galvanized iron from a plank or pipe. Affix a handle. Rattling the iron yields affective thunder. The larger the metal, the more substantial the thunder.