Book 4, Chapter 13:
‘Your dad’s in the paper, Weasley!’ said Malfoy, brandishing a copy of the Daily Prophet, and speaking very loudly, so that everyone in the packed Entrance Hall could hear. ‘Listen to this!’
FURTHER MISTAKES AT THE MINISTRY OF MAGIC
It seems as though the Ministry of Magic’s troubles are not yet at an end, writes Rita Skeeter, Special Correspondent. Recently under fire for its poor crowd control at the Quidditch World Cup, and still unable to account for the disappearance of one of its witches, the Ministry was plunged into fresh embarrassment yesterday by the antics of Arnold Weasley, of the Misuse of Muggle Artefacts Office.
Malfoy looked up.
‘Imagine them not even getting his name right, Weasley, it’s almost as though he’s a complete nonentity, isn’t it?’ he crowed.
Just wondered if this could have possibly been inspiration for the name of Ginny’s pygmy puff two books later.
There’s a good catch, I bet it was!
Also it’s a possibility IRL that either Rowling had the name in mind subconciously, or didn’t think the Pygmy Puff was important enough to warrant a new name. Or Rowling consciously had Ginny subconsciously name her Arnold, as you say.
