How fast JK Rowling wrote the first draft to the screenplay;

the amount of detail the filmmakers put into everything in the movie, even the characters' underwear;

and the moment of serendipity JK Rowling had when choosing the look of the Macusa headquarters.

Stay tuned to hear these fun facts and more as we go behind the scenes of "Fantastic Beasts and Where to Find Them".

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JK Rowling has spent more than 17 years creating the wizarding world inside her mind.

And over the years, she developed back stories for some characters not featured in the "Harry Potter" films, one of which was Newt Scamander.

So when Warner Brothers asked her if she'd like to write a screenplay for "Fantastic Beasts", she was able to immediately get to work and was able to write a rough draft for them after just 12 days.

Veteran "Harry Potter" director David Yates was given the screenplay to see if he might be interested in directing the movie.

He was very interested to read the story, but he told the producer up front that he didn't think he could direct it because he was still worn out after spending six years making four "Harry Potter" films.

However, after reading the script, he immediately changed his mind.

The amount of detail in JK Rowling's wizarding world is what makes her books so special, and the same can be said about the films as well.

Every prop you see in the movie⏤from the maps on the tables to the documents laying on the desks down to the smallest slips of paper⏤were all highly-detailed, just to help the world feel more real to the actors and the audiences.

The same amount of detail also applies to what you don't see in the movie.

For example, one time, Ezra Miller opened up a desk drawer on set in between takes, and he saw that it was filled with archives of newspapers.

Each newspaper had pages of articles, all fully written out, which nobody would ever see because the whole time, they were kept inside a drawer.

The level of detail didn't stop at the props, but also extended to the costumes as well.

For example, it took 30,000 feet of thread to weave Queenie's ombré-colored overcoat, and her costume underneath the coat was designed to look like a classic witch's dress with a little 1920s flair.

Ezra Miller had some 1920s flair underneath the surface with a very detailed set of underwear.

The costume designer sewed some Mesoamerican sacred embroidery onto the back of his long johns just to help him feel even more immersed in his character.

The intricate level of detail didn't just apply to the leading characters, but it was also extended to the extras as well.

The meeting in the inner chamber involved dressing up 200 extras to represent wizards from all over the world, which meant that no two costumes could look alike, since each wizard's culture had to be different from the others to make them stand out.

Since these characters represented the world's highest dignified wizards, they were also dressed to look like one, with ornately decorated costumes that usually would be something a leading man or leading lady would wear.

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Working with hundreds of extras on set can also create a tedious inspection process to make sure everyone stays camera-ready for each take.

For example, while shooting the exterior scenes on the New York City streets, the costume department had as many as 600 extras on set in one day.

They were all dressed for the winter, but were being filmed during the summer, so the extras frequently removed their coats and scarves to stay cool between takes.

This provided quite a challenge for the costumers because they had to inspect all 600 people before each take to make sure everyone was bundled up to avoid breaking the immersion of the scene.

There are very few places in New York today that look like 1927 New York, so all the exterior sets were built on a backlot studio in a T-formation to make filming more efficient.

The street took 15 weeks to build with a crew of over 260 people.

The major locations, such as the bank district, the Macusa, and the tenements were on opposite ends of the street.

When filming any one of those areas, they used green screens to cover up the other parts they didn't need, and then the visual effects team used CG to extend the streets into the background to make it look like all the major areas were miles apart.

JK Rowling always imagined the Macusa headquarters would look like the Woolworth building in lower Manhattan.

She had visited the building before, but it wasn't until she saw photographs of it that she noticed something very serendipitous that related to her wizarding world.

At the top of the arch over the main entrance, there is an owl sculpture, and once she saw it, she knew the Woolworth building would be the right choice to double as the Macusa headquarters.

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