After a wait long enough for several new Gladers to join Alby and company, "The Maze Runner" will finally be hitting Digital HD on Tuesday, December 2; followed by the Blu-Ray and DVD release of the hit movie on December 16.

In honor of that release, MTV News let Wes Ball out of the box -- a.k.a., the busy director took time out his schedule working on the upcoming sequel "The Scorch Trials" to call us from set -- long enough to run down the reasoning behind nine key changes from James Dashner's original novel.

Massive spoilers for "The Maze Runner" book and movie past this point!

1. Teresa And Thomas' Terrific Telepathy

Probably the biggest excision from the book for the movie was Thomas (Dylan O'Brien) and Teresa's (Kaya Scodelario) psychic bond. In the book, the two very rapidly discover they can talk to each other through their minds, as well as sense when the other is in the area. This is actually something that -- spoiler -- plays an increasingly heavy part in the next two chapters of the series, so for fans it was particularly surprising to see this missing.

For Ball, though, it was simply that portraying telepathy on screen just doesn't work.

"Well one, I just couldn’t figure out how to pull it off in a movie," Ball said. "The only thing I could have done was these two characters staring at one another with voiceover happening off-screen, but that just wasn’t going to work."

Citing "Lord of the Rings" as the only movie to successfully make a psychic connection work on screen, Ball decided instead to play up the characters, versus the supernatural elements.

"I felt like the most important thing was that there is this mysterious character, and there was a connection between the characters," Ball continued. "That was the important thing to get across. We tried to do that visually instead of just through sound."

2. Actually Pretty Much Everything About Teresa

In fact, other than the basic character, which is very much the same, a lot about Teresa's arc was tweaked for the movie, from her general timeline, to not, you know, being unconscious for a good portion of the running time. That, like the removal of the telepathy, was by design.

"The biggest thing that guided us to make whatever changes we made were usually about pace, and a grounded sense of realism," Ball said. "The other thing was how do you make that believable. Even with the world itself, making it a little more grounded, then making it totally so massive that it was hard to believe in.

"With Teresa, the tricky thing is that we have six or seven main characters in this thing, so you know giving everyone their screen time and their proper due was a real challenge, but there’s no way we could just have Teresa show up and just be asleep in a hut for half the movie. It was easier to suppress that a little bit, and have her arrival be a real trigger for things... And then bring her into the story much quicker.

"At the same time we knew that we were going to make the second movie, and we were introducing these characters; so we could flesh them out further in the next one. The challenge was giving enough of the characters so that you were intrigued by them and wanted to know more even if we weren’t able to just go into it all."

3. Good Grievers

In the book, the terrifying Grievers that prowl the Maze are described more as slug-like balls of flesh, hair and machine; while in the movie, the equally terrifying (if not more-so) Grievers are more spider-like, with mechanical clicking limbs as well as gross, fleshy bodies.

In this case, it was again how best to make the visuals work for screen, versus the page.

"The best way that I could interpret what James described is kind of like caterpillars, and I just thought that that just wasn’t going to be scary enough for a movie," Ball said.

Instead, the production team looked towards a "universal fear of spiders and just bugs in general," as well as scorpions to design the Grievers.

"I still took all of the same type of cues, where if you look at the design on the Blu-ray you’ll see very clear shots of these things. The body is very much like a slug, this kind of mass of muscle and gross stuff... And then they insert these metal appendages that allow it to be mobile."

4. Whistle While You (Don't) Work

The first third of Dashner's book (approximately) is all about Thomas getting used to his new home in the Glade, trying out different jobs before eventually ending up as a Runner. The movie makes mention of the different positions available, but doesn't spend nearly any of its running time on the day-to-day of the Glade, in favor of getting Thomas running as soon as possible.

For this change, it was all about pacing.

"Things have to get going within 15 minutes otherwise the audience gets restless," Ball said. "Otherwise we have a three hour movie and that just wouldn’t work. There’s always little hints at those things. We have this one scene where Thomas is working in the field... We have the brief mentions of his other jobs. Then the one scene when Thomas goes exploring and they find Vince, so those little elements are in there but we just can’t dwell on them."

5. Griever Go Down The Hole

For certain sections of the "Maze Runner" fandom, one of the biggest aspects of the book is the Griever Hole, the invisible location off the edge of the Maze where the Grievers go to rest during the day. It's a major part of the puzzle of figuring out the Maze, and in the movie is approached entirely differently. There's a hole, it's just not an invisible hole off the side of a cliff.

"Honestly, it was part of that believability thing," Ball said on the change. "I had a tough time resting on an idea of an invisible hole, especially when there’s a cliff.

"In the book they found that cliff pretty quickly. Oh this is interesting, this is different. You kind of knew where this was going. The invisible hole thing, it was just too much for me. And then second, I really wanted story-wise for Thomas to find his way out and to fight his greatest fear, which was the Grievers.

"So, I wanted the Griever to be able to provide something. Actually killing a Griever was the necessary step to further his pursuit to find a way out. It was more similar in concept than visual, but we felt that it was the right choice to make."

6. Numbers Game

Similarly, the solution to the Maze is drastically different from the word game in the book, to the numbers game in the movie. This is one aspect that Ball didn't see as that much different, despite how the two events play out.

"Conceptually, it’s very similar," Ball said. "Hidden in the Maze itself is the way to find your way out, whereas in the book, it was the idea that the Maze was so big that it hid parts of the Maze itself. You actually have to map the Maze in order to find these clues, which is something we have with Minho.

"He is actually able to map the Maze and find these numbers, and that’s why he’s able to make sense of it all. Really, we tried experimenting with how you would actually show this idea, and it just wasn’t visually exciting at all."

7. Where In The World Is The Maze?

We'll actually back off from spoilers a bit here, but in the series the Maze is in a very different place than the desert location we see at the end of the movie. It changes a number of aspects of the Maze, which Ball was happy to get into.

"Firstly, in the book there was a fake sky over them -- and we experimented with that, but visually it looked absolutely ridiculous," Ball said. "Separately from that, in the book they got whisked away in a truck or a van or something. For the whole movie I wanted the perspective of the Maze being... You never cut out far from it. You never see if from some God-like point of view, so that mystery stays alive.

"You needed to understand that size and that scope of the Maze at the end, so that’s why we chose the helicopter idea, so that you could actually see this thing for the first time. Visually it’s much more exciting, I think, and it meant cutting out the whole great sky thing in the book... But again that’s where I thought we went a little too Sci-Fi with it. If they’re using the real weather for this world, and they just can’t see it."

8. The Fate Of Gally

Gally (Will Poulter) goes down in a very, very different way in the book, mind-controlled by WCKD into killing Chuck, and then getting beaten up by Thomas. In the movie, he's hit right through the gut with a javelin, seemingly dying. It also seems to add a finality to, let's say, other elements that play out later in the series. Not so, says Ball.

"We wanted something that was sharp and quick and out of nowhere as well, because there was no way that we were going to do a death and then go deal with Gally," Ball said. "It needed to just kind of build to this one climactic moment where all hell breaks loose. It was just an up-pacing thing, not a storytelling thing. We made it a little more simple and we made it... I won’t give anything away. We made sure that the way we took him out, that there is still a chance. [Laughs]"

9. Why Change Anything?

In case it isn't obvious by now, Ball and the team changed a number of the aspects of the books for believability reasons... But when you're dealing with an enormous Maze constructed to test teenagers in a post-apocalyptic world, why change anything at all? What's the line between what does make sense, and what doesn't?

"It’s a very tough line honestly because there’s this obvious argument where, why would they build this gigantic maze, just to test these kids?" Ball asked rhetorically. "We have our own explanations for our own thing that will play out in the future movies. Even though the Maze does design itself, there’s not crazy holograms, you know it’s not 400 feet tall, it's maybe 150 feet tall.

"Just trying to downsize it into something that is still epic and impressive, but not something that it so far-fetched. Also that feeling that the Maze wasn’t always a Maze. This might have been something else when the world came crashing down, and this was repurposed into this Maze."

"The Maze Runner" is out on Digital HD December 2, and hits Blu-Ray and DVD on December 16.