The Hogwarts portraits are certainly more than just paint – from the ones we meet over the course of the books, they know how to have a bit of fun. So if the subjects of such portraits can move into other portraits, make up passwords, give advice, and challenge the students to duels, you can bet they probably get up to all sorts of other stuff when nobody is watching.
Placing bets on the students
When you’re sitting around for all eternity on a wall, it’d only be natural for the portraits to start playing games with their surroundings – such as secretly placing bets on the Hogwarts students.
In the way that we might watch raindrops race down the outside of windows, for example, maybe portraits like to ‘race’ the Hogwarts students and see which one makes it down the moving staircases first (adjudicated by neutral portraits following the route, of course).
The portraits could even keep a complex league table based on this and other school activities (exam results and the Quidditch Cup, for example). So much happens at Hogwarts, it makes sense that you’d put a wager on things from time to time.
Scaring students back into bed
Imagine you’re a long-suffering wizarding portrait of someone famous, like Adalbert Waffling, and you get woken up in the middle of the night by a bunch of rebel Gryffindors sneaking around. You didn’t waste all that time becoming a legacy to get bothered by a bunch of kids.
Wouldn’t you be tempted to silently flit through other portraits after them, and shout ‘BOO!’ just as they reach a particularly dark patch of corridor? It would be hilarious. Phineas Nigellus’s portrait seems like the type who’d do this sort of thing.
Switching places to see who notices
Although they’re moved around occasionally, the portraits must eventually feel like part of the furniture. What better way to liven things up than seeing which portrait can go the longest pretending to be another? We imagine Sir Cadogan would be terrible at this, sitting in the frame for Violet, the Fat Lady’s friend, talking in a comically high-pitched voice and wearing her hat. Maybe. Who knows!
Teasing the portraits of Gilderoy Lockhart
During his time as Defence Against the Dark Arts teacher at Hogwarts, Gilderoy Lockhart had many pictures and portraits of himself in his office and classroom – in fact, in Harry Potter and the Chamber of Secrets (2002) he was shown to have a large portrait of himself painting a portrait… of himself. Meta.
If you were trapped with several versions of Lockhart, not just in lessons but all through the school holidays, too, wouldn’t you be tempted to make fun of them a little? It’s the next best thing to making fun of the man himself, after all.
Matchmaking their favourite students
When you’re stuck to the same wall every day for weeks you have a lot of time to get to know the students and their schedules.
Over time, perhaps the portraits would figure out which students were nursing crushes, and decide who was right for one another, or who was not-so right. You could even manipulate the circumstances. Imagine an ancient portrait of Merlin stopping a student for a chat because the boy she likes will be coming down the corridor any minute now…
Having wild parties over the summer holidays
We know from the Fat Lady and Violet that magical portraits can enjoy a bit of a tipple, as long as it’s a painted tipple (they consumed several vats of wine from a portrait of some drunk monks). Over the long weeks of the summer holiday they have a theoretically unlimited amount of food and drink, and practically miles of canvas across which to enjoy it. Imagine the wild parties that must ensue.
Kudos to the artists of the original paintings for providing the subjects with enough party favours for a lifetime bash.