Half the sounds in a film are celery
Most of what you hear in a film was not recorded while filming. Dialogue is, but footsteps, rustling clothes, punches and crunching snow are added afterwards by a foley artist, working in a room full of junk while the picture plays.
The trade is named after Jack Foley, who worked in early Hollywood, and its toolkit is famously ridiculous. Coconut shells for hooves, a leather glove flapped for wings, cornflour in a pouch squeezed for footsteps in snow, and celery snapped close to a microphone for breaking bones. It sounds more real than the real thing, which is the entire point.
The clapperboard is a piece of engineering
That board snapped in front of the CAMERA is not a flourish. Picture and SOUND are recorded separately, so the EDITOR needs a single moment that appears in both: a sharp visual bang and a matching spike on the audio track, lined up frame by frame.
The writing on it does the other half of the job. Scene number, take number, production, date — so that months later, somebody staring at thousands of clips knows precisely what they are looking at. The CLAPPER loader who keeps that paperwork straight prevents an extraordinary amount of misery.
Gaffers, grips and best boys
Film crew job titles sound like nonsense and are all literal. The GAFFER is the chief electrician, responsible for every light on SET. The best boy is the gaffer's second in command. A GRIP moves and rigs everything the camera sits on — dollies, cranes, tracks — and a key grip runs that department.
The names survive from the early studios and stuck, leaving a modern film to end with a scrolling list of jobs that sound like an occupations list from 1930. They are all real roles, and on a big production there may be several people doing each one.
Everybody starts as a runner
The entry-level job is the RUNNER: fetching, carrying, making tea, driving things across a city and standing in the rain holding an umbrella over somebody more important. The pay is poor and the hours are long.
It is also, in practice, how most careers in this industry begin. A RUNNER sees every department at work, learns who does what, and is in the room when somebody needs a spare pair of hands. A remarkable number of directors and PRODUCER credits start with several years of carrying other people's equipment.
Why the credits go on so long
A feature film's credits can run ten minutes because hundreds of people each did one specialised thing. The CAST is the visible fraction; behind them sit the SCREENWRITER who wrote it long before anyone was hired, the MAKEUP and COSTUME departments, PROPS, the STUNT team, the location scouts, the caterers and the accountants.
Days are long — twelve hours is normal — and shot out of order, so an actor may film a reunion scene before meeting the character they are reuniting with. Holding all of that in one coherent shape, across months, is the actual job of the DIRECTOR and the PRODUCER.