Nightmares such as Trogglehumpers and Bogthumpers are bad dreams. When caught they appear as red, thrashing storms that violently try to escape.
Both good and bad dreams live in dream country, the BFG often goes there to capture good dreams to blow into bedrooms with his dream pipe. The BFG however, dislikes bad dreams such as Trogglehumpers and Bogthumpers, he keeps them locked away so that they may never frighten children.
Good dreams appear as calm, green sea urchin like clouds that wait patiently in their jars. Bad dreams such as the Trogglehumper however, appear as red, thrashing storms that violently try to escape.
Sophie mentions having a nightmare where she woke up sweating. The BFG explains some nightmares he has captured would have her waking up screaming, her blood turning to ice and her skin crawling along the floor.
- Only two nightmares are shown, the one about giants given to the Queen and the Trogglehumper given to the Fleshlumpeater.
- The BFG is shown to be able to mix dreams together to make nicer dreams or frightening nightmares.
- In the 1989 animated film, Trogglehumpers can effect people or giants even when they are wide awake, based on the Fleshlumpeaters immediate reaction to the nightmare, Trogglehumpers can even cause hallucinations.