Okay, dudes, I’d like to point this out. This is a photo of Toothless after Torch had bitten his tail in Terrible Twos. I absolutely love the lighting of it. I have this theory. The bright side represents of the present while the dark represents scars from the past. That bite reminded him of the pain that went through his tail when he lost his left fin. It also reminded him that he couldn’t fly the way he used to without Hiccup’s help. I can imagine that must’ve been really painful to deal with, considering that he’s been flying his whole life.
Not to mention my head canon that Toothless has lost his nephew to one of those typhoomerangs long ago and that his nephew was his only family left…until Hiccup came along of course.