well as a special organ hidden deep inside their body that is designed to heal the orc, even capable of bringing them back from some types of death. Featured in Unseen Academicals. (Other definitions) Trolls Trolls on the Discworld are, essentially, living, mobile rocks. Consisting largely of silicon, Discworld trolls vary in intelligence depending on their body temperature (as silicon heats, it loses efficiency; thus, 'keeping a cool head' is a literal fact of troll existence). Trolls have grown to overcome those vicious stereotypes of yore and have lived very prosperous lives in heavily populated cities with (relatively) little killing. (Other definitions) Undead Species in the Discworld novels categorised as undead include: Banshees (Celtic folkloric definition), Bogeymen (Other definitions), Ghouls (Other definitions), Ghosts (Other definitions), Mummies (Other definitions), Vampires (Other definitions), Werewolves (Other definitions), and Zombies (Other definitions). In the case of zombies, they are (unlike the classic horror-fiction depiction) fully sentient; for many of them, 'dying at their desk' merely presented a minor inconvenience and a chance to request bereavement leave on behalf of their families. (Other definitions) Other life forms Pratchett also created a variety of other fictional life forms on the Discworld. Like the sentient species, these also have real-world connections, although most of these connections take the form of slight changes to existing real-world animals, as shown in the .303 bookworm, which is a worm that evolved differently due to the danger of consuming magic books, or the hermit elephant, which is an elephant who has evolved hermit crab-like living conditions. Calendar The Discworld's Unnamed Continent's fictional calendar was first defined in a footnote in The Colour of Magic, and has been expanded upon in later novels and The Discworld Almanak (2004). It has numerous oddities, the chief of which is its length. The calendar is based on a Great Year, or Astronomical Year, defined as the time it takes for the Disc to revolve once on the backs of the elephants. This lasts 800 days and contains two of each season (Midsummer occurs at a given point when the sun passes directly overhead, midwinter when it passes perpendicularly. However most people, especially farmers, consider four seasons to be a year, so an Agricultural Year of 400 days is used for most purposes. The agricultural year is divided into 13 months: Ick (16 days) (the "Dead Month") Offle (32 days) February (32 days) March (32 days)