"Vermithrax Pejorative" roughly translates as "The Worm of Thrace Which Makes Things Worse".
This was the first movie to use go-motion, a variant of stop-motion animation, in which parts of the model (in this case, the dragon) were mechanized and the movement programmed by computer. During shooting, the computer moves the model while the camera is shooting, resulting in motion blur, which makes the animation more convincing.
Vermithrax's dragonfire was achieved with two flame throwers designed and built by Brian Johnson. Both used a gas under high pressure, laced with lycopodium powder; this caused the brightness and particular colour of the flames. The first, cannon-sized flame thrower was swivel-mounted; it was used in the wide shot in the Lake of Fire, and in the confrontation with Ulrich. Previously, an internal incendiary system had been installed inside the full-size dragon head, and although successfully tested, it proved unsatisfying on the actual stage. As a result, the fire was shot separately and optically composited with Vermithrax -- whatever version of it -- when it unleashes its fiery attack. The second flame thrower -- of smaller size -- was used for closer shots where the reach of the larger one was not required.
Some of the score by Alex North was music he'd originally composed for 2001: Odissea nello spazio (1968) that went unused.
George R.R. Martin, author of the "A Song Of Ice And Fire" novels, upon which Il trono di spade (2011) is based, has said that Vermithrax Pejorative is "the best dragon ever shown on film." One of the deceased dragons mentioned in the 1st season of the series, by Viserys Targaryen, was named "Vermithrax".