He is Groot.
How did Vin Diesel know how to put just the right touch of emotion in every I, am, and Groot? According to Guardians of the Galaxy director James Gunn, it’s because he had a special script that revealed what the taciturn tree-man was actually trying to say. It was apparently top-secret: As Gunn told a fan on Twitter, “Only Vin and I have the special Groot script with translations of what he’s saying.†Or, as Groot might have put it, “I am Groot.â€