Guardians of the Galaxy 2: How Vin Diesel knows what Groot is saying

There's a reason Vin Diesel is able to convey so much emotion as Groot, even though his character can only say a few words.

Director James Gunn shared a photo of the special "Groot version" of the script for Guardians of the Galaxy Vol. 2, which he says only he and Diesel ever get to read. It contains the meaning behind all of the character's lines, although everyone else just hears him say "Groot."

As ScreenRant points out, that means it's likely that all the other actors don't actually know what Groot is saying in the original 2014 flick or the upcoming sequel.

Meanwhile, Diesel recently watched a sneak peek of the eagerly anticipated Marvel film, and he shared his reaction on Facebook Live. He spent the first few minutes in awe, barely able to say more than a few words himself.

"What I saw just now is like seeing Santa Claus in September, because you want Christmas to be tomorrow," he said. "I can't believe you have to wait this long to see this movie."

Gunn was there to witness Diesel's response, and he said there's a lot of heart behind the blockbuster film series. "The first movie was really about becoming a family. This movie is about being a family," Gunn said. "And what's harder: becoming a family or being a family? I think it's being a family. That's where you really have to deal with each other."

Diesel said Guardians of the Galaxy Vol. 2 will "blow your mind" when it premieres May 5, 2017. Check out 20 facts you probably don't know about the comic book and first movie.