Simplify the following text for a Grade 5 native English-speaking person.
Original: In Norse mythology , Gram ( Old Norse `` wrath '' ) is the name of the sword that Sigurd ( Siegfried ) used to kill the dragon Fafnir .
Simplified: The unit of measurement is at gram In Norse mythology , Gram is the name of the sword of Sigurd ( Siegfried ) . He used it to kill the dragon Fafnir .