Attack on Titans Reiner actually screams a name when he transforms
The Titans are humanoid monsters with an appetite for human flesh – the series’ Japanese title, Shingeki No Kyojin, translates more accurately to Progressive Giants. They are so starved that humanity is (allegedly) nearly extinct and the survivors all live behind three layers of walls; The ruling class lives behind the innermost Wall Sheena, the middle class behind Wall Rose and the lower class behind the outermost Wall Maria.
The story begins when two Titans, one skinless Colossal and one with tan armor plates, tear down Wall Maria. This strategic attack is the first clue to the terrifying truth: Titans are actually transformed humans. A few, so-called Titan Shifters, can control their transformations and also have special powers. During his first fight as a scout, Eren discovers that he is a shifter. It turns out that the Colossal and the Armored are part of a group of shifters sent to exterminate humanity within the walls. Worst of all? It turns out that the former two shifters are actually Eren’s friends Reiner (the Armored One) and Bertholdt Hoover (the Colossal).
While the Titan Shifters retain their personalities and self-control when transformed, most of them do not speak. Instead, they yell. The sound of that roar is one of the biggest differences between the Japanese original and the English dub.