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.

Gobber has a total of fourteen different hand attachments throughout the film.

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 hesitation Toothless shows during the famous "touch" scene was actually an animation error. However, it looked so perfect that the animators chose to leave it in the film.

When Hiccup reads the Dragon Manual, the writings in it are actually in plain English cryptographed into runes. With little effort, you can read what Hiccup is saying, e.g. "Speed Unknown."

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 character Stoick is 7'2" tall.

Hiccup is left-handed, as demonstrated when he is writing in his journal/sketchbook.

According to Chris Sanders and Dean DeBlois, they were present when the orchestra played the cue "Romantic Flight" the first time. Upon completion, the orchestra broke out into applause.

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.

There is a drawing very closely resembling the Flux Capacitor from the Back to the Future (1985) movies on Hiccup's design board.

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.

Hiccup is the only character to refer to Toothless by name.

The hammer used by Stoick bears a strong resemblance to the Marvel comics version of the hammer Mjolnir, wielded by Marvel's Thor. The traditional mythological hammer of Thor looks much different.

The first film released in Technicolor 3D, the company's 3D system that works with standard 35mm film projectors.

The scene where Toothless learns to smile was inspired by an animator's infant son learning to smile.

Hiccup is the first teenage protagonist in a DreamWorks Animation film.

The creature sounds and audio effects in the film were mostly created at Skywalker Sound.

Box office of the film almost reached around $500 million worldwide.

Due to popularity from this films release, many animal shelters reported that many black cats were adopted & named 'Toothless'.

Jay Baruchel co-starred with T.J. Miller in She's Out of My League (2010), which was released just two weeks prior to How to Train Your Dragon (2010). He would later also co-star with Christopher Mintz-Plasse and Jonah Hill in This Is the End (2013).

Lost the Oscars it was nominated for to Best Picture nominees. It lost Best Animated Feature to Toy Story 3 (2010), and Best Original Score to The Social Network (2010).

Charlotte Dujardin used the music from this film in her Olympic Gold-Winning Dressage Freestyle in the London 2012 Olympics.

First Dreamworks Animation movie to have the new Dreamworks Animation logo that is currently used in the 2010's, it is also the first film to have a logo gimmick in that new logo.

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.

First film by DreamWorks Animation to be released in the 2010s.

The only non-Best Picture Oscar nominee that year to be nominated for Best Original Score.

Helheim's Gate is a reference to the Norse goddess Hel. She is the daughter of Loki and guards the gate leading to Hell.

The only film in the franchise to not be released the same year as a Lego Movie film. On the other hand, How To Train Your Dragon 2 came out in 2014, which is the year the first Lego Movie came out, and How To Train Your Dragon 3 will be released in 2019, the same year as The Lego Movie sequel.

David Tennant: the narrator of the How To Train Your Dragon audio book series, provides the voice of Spitelout, though he is not credited. He also narrates some features on the film's website.

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).

When the vikings celebrate, after all of the dragons fly out of the volcano, nearly all of them are holding their swords left-handed.

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.

Toothless losing part of his tail foreshadows Hiccup losing his leg.