In How to Train Your Dragon, what injury causes Hiccup to use a prosthetic leg?

In How to Train Your Dragon, Hiccup uses a prosthetic because he is missing his left leg.

Hiccup loses part of his left leg during the final battle of the first film, when he and Toothless escape the destruction surrounding the Red Death. Toothless also suffers a serious injury, leaving him unable to fly without assistance. Hiccup later designs a prosthetic foot that connects him more closely to Toothless’s artificial tail fin.

The parallel injuries are central to the story’s message about cooperation. Neither character can function as before, but together they develop equipment and techniques that let them fly. Hiccup’s prosthetic remains visible in the sequels and becomes part of his design rather than being treated as a temporary plot detail. The injury is to his left leg, not his right, and he does not lose an arm. The films use the disability to show adaptation, engineering, and mutual dependence.