the_debt_of_time

"As this is your sixth year, we will begin instructing you on how to use non-verbal
spells. It is a poor wizard who needs to speak a charm in order for it to work properly. Pair
up."
In the earlier years of Defence, the pairs had been friendly. As the Slytherins and
Gryffindors grew older, though, the animosity intensified, and soon the classroom was split
down the middle with red and gold on one side, silver and green on the other.
While Professor Higgs had always paired James and Sirius together, Professor
Scrimgeour did not know better. James stood across the room from Severus Snape, a grin
on his face, while Sirius was all too eager to take a crack at Amycus Carrow. Mia stood to
the right of Sirius, glaring across the way at Elora Zabini, and beside her, Remus was staring
at Alecto Carrow.
"Now, Gryffindors will attempt to jinx their partner while the Slytherins will
attempt to protect themselves. Not a word is to be spoken," Scrimgeour said fiercely. "On
the count of three. One, two, three!"
All at once, Amycus, Elora, and Alecto flew backward into the wall behind them,
stunned to the ground. Sirius, Mia, and Remus shared a proud grin over their non-verbal
spells.
James stared intensely across the room as he and Snape faced off in a non-verbal
duel. Snape had erected a shield in time, of course, but instead of a simple stunning spell,
James was trying to silently penetrate the Slytherin's shield, forcing it back on him.
Everyone stopped to watch closely as hazel eyes met black and the two boys glared at one
another viciously.
"Stop!" Professor Scrimgeour yelled minutes later, and both Snape and James
released, nearly collapsing to the ground after forcing their magics to press so hard against
one another. "While showing impressive strength, Mr Potter should have used additional
attacks, layering spells instead of forcing one that was not working. Mr Snape, you should
learn to hold a shield and fire hexes simultaneously. It could mean your very life when
faced off against a Dark wizard."
Sirius clenched his fists and scathingly muttered, "Except that he is a Dark wizard."