Faliure to do so will result in the victim being killed in one way or another by the Geas.
Used alot by Celtic Shamans and Norse Guayla (witch doctors). Not used offensively as any magic user able to preform a Geas can easily destroy enemies in a multitude of other ways.
Allan (white): gea gea
Jamal (guess): WTF DONT TRY AND SOUND LIKE ME!