We’re sitting on picnic chairs, huddled in a tight semi-circle around a monitor, watching a scene from Fantastic Beasts being filmed. It’s dark and all is quiet on set because the camera’s rolling and actors are acting.

The sound of ‘Cut!’ means we can exhale and whisper a little among ourselves. That is, the make-up artists, the hair stylists, the stand-in guys, the extras and me. These are some of my greatest gossip sessions, these chats between scenes.

Katherine Waterston’s make-up artist is telling me how actors keep their skin flawless for close-ups, when… ‘Get the best boy over here,’ comes a voice from the darkness to my left, where some of the production crew are gathered.

There’s a scuffle, some murmuring into a walkie-talkie and a man in boots, holding some cables, materialises. He disappears into one of the little tents set up in this lot, where heads of department congregate and whisper important things about movie-making to each other.

‘The best boy,’ I gasp. ‘He must be the best boy.’

I’ve always wanted to know exactly what a best boy does. What, precisely, are they best at? Is there a secret hierarchy of average, good, great and best boys? Are there any best women? When does a best boy become a best man? Who decides? Is there a panel? Have they ever thought about forming a band called the Bestie Boys?

Today is the day we get answers.

It turns out, there are actually two kinds of best boys (which sort-of ruins the omnipotence I had imagined for The Best Boy™, but never mind). There’s a best boy for the electrical department and a best boy for the grip department. They are second-in-command to the ‘gaffer’ or the ‘key grip’. The gaffer is the head of electricity on set and the key grip is in charge of building, moving and maintaining all the equipment that carries the cameras.

Legend has it they were called 'best boys' because, back in the day, the people rigging up lighting, electricity or cameras would yell out for a bit of assistance by asking someone to send them ‘their best boy’. As in, the best qualified person from their team for the job at hand. So it is a measure of merit, but it’s not quite as survival-of-the-fittest as I had half-imagined.

As for women in the role? Well, it depends really. Sometimes they might be called best women or they keep the title best boy because that’s just what it’s called.

My favourite thing about gaffers, grips, key grips, dolly grips and best boys is that it’s a bit of a family business. The gaffer on Fantastic Beasts told me that he was once a best boy, his dad was one, and his dad’s dad was one. It’s the type of skill that tends to get passed down from generation to generation.

Imagine a whole family line of best boys. How proud you’d be.