It wasn't like Mo felt that he'd completely mastered this spell, and already he was being asked to put his new skills to the test. And not something nice and easy... an object falling to the floor, ideally lethargically. No, the professor was throwing something right AT him. Right at Mo's face.

He didn't fancy the idea at all.

Still, he took his place in line and practiced the waving as he muttered the incantation over and over. It wouldn't be the worst thing in the world to take a water balloon to the face in front of his classmates. He'd still prefer avoiding it. Mo took his turn at the front of the line, forcing himself not to close his eyes in anticipation of the water balloon.

Come on, man! He didn't close his eyes when there was a Bludger zipping towards him, and that was a much bigger deal than a measly water balloon. He lifted his hand, pointed it in the professor's direction, and waited for the balloon to fly at him. A moment later, when it did, Mo waved his wand, "Arresto Momentum!"

It worked! The water balloon shimmied a little in mid-air, but it stopped in place. Mo grinned broadly as he snatched the balloon out of the air, although his grin faltered when his overly exuberant snagging of the balloon ruptured it right in his hand. At least it wasn't his face, right?

He surreptitiously wiped the water from his hand as he moved back to his desk to gather his belongings. "Thanks for the lesson, Professor."