I'm not sure specifically as I haven't read a novel named 'eucalyptus novel'. It could be about eucalyptus trees, perhaps their ecological significance, or it could be a story where eucalyptus trees play an important part in the setting, like a mystery set in a eucalyptus forest.
Basically, sarcoptic mites and mange mites are one and the same. Mange is the disease that results from an infestation of these mites. The mites burrow into the skin, causing irritation and various symptoms.
The significance of the monster spray in the story is that it gives the characters, usually children, a sense of control over their fear. Instead of being helpless against the idea of monsters, they have a tool, the spray, to combat it.
Most of the time, mange is indeed triggered by mites. Mites burrow into the skin, causing irritation, hair loss, and other symptoms. Different types of mites can lead to various forms of mange.
This scene usually appeared in period comedies, where two people competed to pee in the toilet. One moment, they would spray the toilet, and the next moment, they would pee again and again. This behavior is often seen as a funny way to make people laugh because people often encounter various difficulties and challenges in the toilet, such as not having enough space or not having the right facilities.
In a novel, such a scene might describe two people using various skills and strategies to win a game in the toilet. They may use various props and tools such as sprayers and urine pump to increase the difficulty and fun of the game.
This kind of scene was usually designed to increase the comedic effect and portray the character's image so that people would feel relaxed and happy when watching movies or TV dramas.