Such as a hidden cameo of two characters who were cut from the story, mistakes that Emma Watson and Daniel Radcliffe made during the Yule Ball, and you'll get a glimpse of the secrets behind the visual effects of the Triwizard Tournament.

The screenwriter and the producers decided to condense JK Rowling's 734-page book into a 2.5-hour movie, which meant a lot of subplots and characters, like the house-elves Dobby and Winky, had to be cut to tighten the pace.

However, you may not have noticed that the two elves had a hidden cameo appearance as they rode past the screen on llamas during the Quidditch World Cup.

The reveal of Hermione's dress at the Yule Ball was an important moment for her character arc, and the costumers altered Emma Watson's dress over and over again to get it to look just right.

When the dress was finished, Emma was so worried about ruining it that she decided to never sit down while she had it on.

However, her careful nature was literally her downfall, because during one take of walking down the stairs, she didn't make it more than three steps down before falling in front of everyone on set.

Even though her pride was hurt, the dress didn't get damaged.

All the young actors had three weeks to learn the dance choreography for the ball except Daniel Radcliffe, who had only four days because he was working on another scene during the dance rehearsals.

So now you know why he was filmed from the waist up, because they needed to hide all the mistakes he was making in his footwork.

For the first task of the Triwizard Tournament, a massive maquette model of the Horntail dragon was made with an impressive 14-foot wingspan.

And then after that, the model was scanned into a computer to create a CG version of the dragon.

To film the second task of the Triwizard Tournament, the crew built a huge 20-foot tank specifically for this movie that could hold 500,000 gallons of water.

As you know, movies need to be lit, even the underwater scenes.

So if you're curious how they lit up a 20-foot, 500,000-gallon water tank, they built an outer wall using dozens of fluorescent tubes to shine on the outside of the tank to make it glow on the inside.

Daniel Radcliffe trained for six months to learn how to dive for the underwater sequence.

The whole thing took three weeks to shoot, and by the end of it, Daniel had clocked in a total time of 41 hours and 38 minutes spent underwater, and he also had to deal with two ear infections during that time.

To film the third task of the tournament, large sections of the hedge maze were built to give the actors something physical to interact with.

The walls of the maze were between 25 to 40 feet high, and the paths were only five feet wide in order to create a claustrophobic feel for the shots.

Ralph Fiennes was the first and only actor considered to play Voldemort for his big reveal.

However, just like many of the other adult actors in the film series, Ralph Fiennes also didn't know much about the Harry Potter books before accepting his role in the movie.

Even though Voldemort's face is more snake-like than it is human, Ralph Fiennes' actual face wasn't covered up with as much prosthetics as you might assume.

He only had to wear one prosthetic to hide his eyebrows, and the rest of the facial features were altered with CG.

Voldemort's eyes are red in the books, but their color was changed for the movie because the filmmakers believed the Dark Lord had to look more human in order for the audiences to be more afraid of him.

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