- "When the decorations went up, Harry noticed that they were the most stunning he had yet seen inside the school. […] the suits of armour had all been bewitched to sing carols whenever anyone passed them. It was quite something to hear "O Come, All Ye Faithful" sung by an empty helmet that only knew half the words. Several times, Filch the caretaker had to extract Peeves from inside the armour, where he had taken to hiding, filling in the gaps in the songs with lyrics of his own invention, all of which were very rude."
"O Come, All Ye Faithful" was a Christmas carol. In 1994, when the Christmas decorations were put up around Hogwarts Castle, the suits of armour were bewitched to sing carols, but had difficulty in remembering all the words. Peeves was known to hide inside the armours and fill in the gaps in the songs with rude lyrics of his creation.
- Harry Potter and the Goblet of Fire (Mentioned only)