the_debt_of_time

The morning of James and Mia's birthday, after opening the gifts that the owls flew
in from their parents as well as the few treats that were given to them from their friends,
Mia smiled deviously up at her brother.
"I have a birthday gift for you. Does everyone know how to do a Heating Charm?"
she asked. "And can you keep it subtle?"
"Did you do something bad, kitten?" Sirius asked with a grin.
Mia only smiled innocently in response.
He barked a laugh and grabbed his wand, motioning the others to do the same.
"Oh, this should be good."
"Now, everyone aim your wands to the Slytherin table and use a Heating Charm.
Not hot enough to burn or scald, but... uncomfortably hot," Mia emphasised.
As one, the Gryffindors swished their wands and uttered the incantation, putting
focus on the green and silver table at the other end of the Great Hall. At first, nothing
happened and Sirius looked disappointed. They kept on with the incantation and suddenly
there was a quiet Pop!
Followed by several more.
Pop! Pop! Pop!
Mia snickered as she watched Snape look up from his breakfast and cast a glance
around the table. Amycus Carrow followed suit.
Pop!
The older Slytherins were looking around, trying to find the source of the noise.
Pop! Pop! Pop!
"What's happening?" James asked with a grin.
Mia beamed. "Just watch."
Pop! Pop! Pop!
One by one, the Slytherins stood from their seats, confused and
shouting. Pop! Some were struggling with their robes—Pop!—trying to get them off as
quickly as possible.
All of a sudden, freshly popped popcorn kernels began shooting out of the lining
of the Slytherin robes, overflowing their pockets and collars, covering their table and
blanketing the floors.