Obviously, someone hadn't been listening, or perhaps they'd been listening all too well. The moment Selwyn had his back to the students he heard a bang, followed by a yell. Then the noise level rose significantly, though he wouldn't have thought it was even possible.
He spun round in time to see the Hufflepuff's snidget soar across the room, followed closely by a niffler, and the sight made him immediately relax. This was what classes should be like. Complete chaos.
The doors of the barn slammed shut with a crash to prevent the animals' escape and Selwyn summoned a clutch of broomsticks to the room.
"All right! New assignment!" he declared over the noise. "Catch the snidget for 150 house points!"
Welcome to Creatures Quidditch. Selwyn will be your referee, Ariane will sit out (as she's my character)
Score by trying to catch the niffler (quaffle).
Other creatures spontaneously escaped! Prevent your opposition from scoring by trying to catch another creature and getting between them and the niffler
Ariane will post spotting the snidget at a random time and the first person to post after her will catch the bird & win the house points.
Selwyn will post regularly telling you if your scoring / keeping is effective.