User blog comment:Llama919/Possible Beast Titan Identity?/@comment-26056057-20150621092722/@comment-5774380-20150621203425

I also thought that burn mark was simply due to the heat of his Titan form. Every time Eren is seen leaving his Titan form, he has burn marks all over his face, and this guy is shirtless, so it's natural that he burned his arm... But I don't know why he doesn't have more burn marks besides that, not even in the face. Hopefully in the next chapter we could find a clue.