Remus was staring at Sirius with a sappy, moonstruck grin on his face. It is Transfiguration, and they are turning hedgehogs into marshmallows. Remus had no idea when he'll use this in real life, but doesn't question it as it gives him the perfect opportunity to watch Sirius play with a hedgehog. His own hedgehog is fast asleep and snoring.
James transfigures his hedgehog faultlessly, a perfect white marshmallow in its place. Professor McGonagall nearly smiles, and he grins, ruffling his hair, and glances over at Lily, but she isn't even looking. Sirius just continues to coo as his hedgehog licks his fingers, squeals when it runs up his arm. Remus thinks this is utterly adorable, and absent-mindedly transfigures his still unconscious hedgehog.
A Hufflepuff in front of Sirius turns around. Sirius says something and she giggles. Remus shakes his head, looking away: she is very pretty.
Gazing down at his own hedgehog, he sighs. This is the consequence of not paying attention when performing magic: his hedgehog is a marshmallow, it's just rather brown, and has toothpicks in place of spikes. Remus isn't sure, but thinks it may also still be snoring.
It is returned to its hedgehog state, and Remus stares at it, intrigued; it is still snoozing.
McGonagall walks by, and he hastily swishes his wand. A small marshmallow is produced, still annoyingly a little brown, but he gets an approving nod.
Softly, he strokes the top of the marshmallow, thoroughly convinced that a tiny snuffle is coming from it.
He glances over at Sirius: he is still talking to the pretty Hufflepuff.
A small sneeze brings him out of his reverie, and Remus quickly changes the marshmallow back, just in case it came from the drowsy creature. Amazingly, its eyes are still shut when he ends the incantation.
However, after being in its original body for a minute or two, cracks opens its eyes, and blinks sluggishly. It shuffles around on the desk, clambering over to Remus. He crouches down to its eyelevel, and locks gazes. The hedgehog nuzzles their noses together, and coughs.
Turning around at a tap on the shoulder, he sees Sirius standing above him, looking fondly down at him with a shy smile.
Palms open, Sirius offers up his own ex-hedgehog. It is a marshmallow, like the assignment asked for, but is surprisingly pink, and heart-shaped. Remus knows that, inside, it will be fluffy, and gooey, and excessively sugar-filled.
He thinks it is an accurate representation of his own heart.