The Marauders arguing over which House the characters would be in. James bursting out into 'You can Fly' while playing Quidditch. James singing 'Bibbity Bobbity Boo' in Charms while Remus face palms. - Imagine if Walt Disney was a wizard.
Actually, we Potterheads know this is not Professor McGonagall because this cat does not have the markings around the eyes that resemble her spectacles. Also as if it's perfectly normal for a cat to be reading a book