Kanske orsaken till att effekterna förändras beror på hur magiker fungerar i Harry Potter ...
Det finns en drivkraft bakom magi och det är känslor.
I varje exempel kan guiden använda mer eller mindre känslor ...
Magic som beskrivs i Wikia om känslor.
A witch or wizard's emotional state can affect their inherent abilities. For example, Nymphadora Tonks temporarily lost her power as a Metamorphmagus after suffering severe emotional turmoil and sadness over her grief for the death of Sirius Black, and when Remus Lupin would not return her affections. In effect, the form of her Patronus changed to reflect her love for him. The form of her Patronus changed to reflect her depression. In 1995, when Mad-Eye called her by her first name, her hair temporarily turned red. Wizardkind are also weakened when in the presence of Dementors for prolonged periods, as said creatures attack their prey psychologically by making them recall their worst memories, leaving the victims physically vulnerable.
Kanske när olika guider lägger på vissa stavar, förklaras förändringarna av den specifika guidens känslomässiga tillstånd.
Ett exempel skulle vara att Harry försökte slåss mot Voldemort med sin Expelliarmus mot den mörka Herrens förbannelse. Den här duellen kommer att drivas av många känslor, vilket kanske ger effekterna av stavningen en mer kraftfull utseende och effekt.
Som sagt av wikia också ..
Several magical spells involve the use of emotion when casting them. The Patronus Charm, for example, requires the caster to concentrate on a happy memory. Force of will under extenuating circumstances also helps in casting spells, and affects the force with which they are cast. An example of this is when Harry is able to conjure a corporeal Patronus when Sirius Black is in danger of being administered the Dementor's Kiss.
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