It was another STEALTH MODE kind of day, and Peeves and his book were doing some invisible traversing of the corridors.

Oh! What was this? Shenanigans? Hijinks? Mischiiieeeeef?

An opportunity was what it was. With invisible book in invisible hand, Peeves cast a little invisible hocus pocus at one of the students (Maria), before invisible floating off on his merry invisible way. A gleeful distant cackling was the only other evidence he'd left that he'd been there at all. "Heheheheh!"