In the book of "How to Train Your Dragon," Hiccup does not have a love interest. Furthermore, Toothless, the dragon in the book, is about the size of the Terrible Terror breed, and he is also green and red, not black. Toothless also got his name because when Hiccup first found him, he had no teeth. He grew one tooth, only to lose it shortly later. The producers decided, with the approval of author Cressida Cowell, that it would be more cinematic to make Toothless large enough to be ridden as a flying mount. As such, Toothless was completely redesigned as a rare Night Fury, a highly intelligent breed of dragon evolved for speed and stealth. His personal name, in the film, derives from Hiccup's observation about how his teeth are normally retracted into his jaws so they don't interfere with his fire breathing, which is typically projected as an explosive pulse.
The appearance and personality of Toothless was inspired by cats, dogs, and horses. The face also bears some resemblance to the giant salamander, the largest amphibian in the world. The shape of his face is also reported to have been based on the face of Stitch from Lilo & Stitch (2002), also directed by Chris Sanders and Dean DeBlois.
The Night Fury dragon species was originally going to be be more wolf-like in appearance. Instead, a Dreamworks employee's computer screen saver of a black leopard inspired the film's creators to make Toothless more feline in appearance.
During the popular DreamWorks intro part of the movie, where a boy on the crescent moon is holding a fishing pole, the shadow of the Night Fury flying through the star-filled background can be seen for a brief moment.
The sounds of Toothless (the Night Fury) are a combination of various sounds, including the voice of Supervising Sound Designer Randy Thom, elephant seals, elephants, horses, tigers, and even domestic cats. The elephant seal sounds used were recordings of elephant seal pups at The Marine Mammal Center in Sausalito, CA, a marine mammal hospital that rescues, rehabilitates and releases sick and injured seals, sea lions, whales, and dolphins.
The name of the village, Berk, is a British derogatory term derived from the cockney rhyming slang "Berkley Hunt." "Berk" is commonly used as an affectionate put down for a fool by people unaware of its true origins.
The sounds the Terrible Terrors make, including growling, are actually based upon a purebred Chihuahua named Paco from Cottage Grove, Oregon. Nia Hansen, a sound designer at Skywalker Sound, contacted his owners after seeing a video of Paco on YouTube, and Paco was paid $100 for his voice work.
This was the first DreamWorks Animation film with a musical score composed solely by John Powell, since he previously collaborated with other composers on Antz (1998), The Road to El Dorado (2000), Chicken Run (2000), Shrek (2001) and Kung Fu Panda (2008). The score was so universally acclaimed, it resulted in Powell's first Oscar nomination for Best Original Score.
Many of the flying scenes are clearly inspired by combat and aerobatic aircraft. Toothless performs many recognizable aerobatic maneuvers such as loop, snap rolls and combinations. For example, when Astrid is taken for her spin, Toothless performs a loop while being "filmed" from near his wingtip. This is very similar to countless sailplane films with cameras mounted on the wingtip.
The village name of "Berk" is remarkably similar to the four-letter Meteorological Atmospheric Report (METAR) report code for Reykjavik Airport in Iceland, which is BIRK. The village of "Berk" could be considered an airport, of sorts.
The trivia items below may give away important plot points.
The film was originally intended to end with Hiccup largely unscathed after the climactic battle. However, the directors decided that it would not feel believable that the heroes could defeat such a formidable foe like the Red Death Dragon without great cost. With that in mind, they decided to have the boy lose part of his left leg at the end of the battle, in a deliberate parallel to how Toothless the Dragon lost his left tail fin, earlier in the film. Whatever concerns about how parents would react to the hero of a family film being so maimed were settled in the film's test screenings. Parents in the audience told the producers on their own accord that they approved of that story development and requested that it be kept in the final edit. In addition, the original book's author, Cressida Cowell, praised this ending and considered it true to the spirit of her book. Furthermore, the scene originally had Hiccup alone as he comes to grips with his wound. However, when Steven Spielberg saw the original footage, he felt that Hiccup and Toothless' interaction in the film's final act had been reduced to something like a mere cowboy and his horse. So, he suggested that Toothless be with the boy in that particular scene so as to reinforce the idea that their companionship was far deeper than that.
According to the audio commentary, when Hiccup, Astrid and Toothless are flying to Dragon Island and are surrounded by all the other dragons, one of the dragons is carrying Gloria, the hippo from Madagascar (2005).
Hiccup's exact age is never given in the film. However, in How to Train Your Dragon 2 (2014), which takes place five years after How to Train Your Dragon (2010), Hiccup is said to be 20 years old. This would make him 15 years old in this film.