The castle itself seemed delighted to have such well-executed magic living within it.

The greenery Fred and George had left behind was truly a masterpiece. It was as much a 'farewell,old chap' to the castle as it was to the students; a testimony to their skills, their penchant for rule-breaking.

Hogwarts had aided and stumped them, let them in and kept its secrets, having gotten along remarkably well with the twins.

The portable swamp they left behind was nearly a formal declaration of affection and gratitude.
The castle murmured, content.