Infernal Combustion Enigma

Mentioned in The Colour of Magic, this is a powerful spell, whose name parodies the phrase "internal combustion engine". It was apparently one of the most destructive spells in the Arch-Astronomer of Krull's magical repertoire. He was about to cast Vestcake's Floating Curse on Rincewind and Twoflower (who had taken the place of two chelonauts about to ride Krull's first space ship over the Edge) when a sinister dome of seaweed appeared and attacked everything in sight. The Arch-Astronomer quickly dismissed the Floating Curse and fired this spell instead.

Despite the immense power of the Infernal Combustion Enigma, all it did was burn away the seaweed in a massive explosion to reveal a box on legs, ominously moving towards the Arch-Astronomer... All the magic of all the assembled wizards of Krull was unable to stop it. And the Luggage does not take kindly to being shot at - despite that shot doing absolutely nothing whatsoever.

Annotation

The spell's name parodies Roundworld's Internal Combustion Engine, i.e, a car engine or train engine. This is not the only time Pratchett does so, however. Leonard of Quirm also built an external combustion engine in Jingo. Unlike the Infernal Combustion Enigma, however, Leonard's invention bears some resemblance to the Internal Combustion Engine - except it used pellets of gunpowder, and it blew up when tested.