As Hermione, having just come home from work, stepped into the living room and found her husband, with his wand in his hand, on the couch with an odd mixture of happiness and misery on his face she got worried. She hadn't often seen him like this. She wondered what was on his mind.

Draco, upon seeing her, rose from his seat and held out his wand.

"I've done it," he said quietly. "I finally managed to do it."

"Do what?"

"It's not just mist anymore, it has a form."

Hermione gasped, finally understanding what he meant. The patronus charm was something he had struggled with for a long time. It wasn't that he lacked the skills, thanks to his upbringing he had become an extraordinarily skilled wizard. The problem was that he hadn't been able to find the right memory. Not even the memory of their wedding day had seemed to work, being buried among all those memories of his strict upbringing and death eaters and all the pressure of being a Malfoy heir. She wondered what it was that had finally made it work.

"But why are you looking like that then?" she asked him, referring to the obvious annoyed expression he bore.

"If I show you my patronus will you promise me that you won't laugh?" he asked, looking at her pleadingly.

"Draco I don't care what form it has, I'm just happy that you finally mastered the spell."

"Just promise me," he said.

"Alright," Hermione said. "I promise, now show me." She had a hard time keeping the excitement from her voice.

"Expecto Patronum!"

What came out of his wand made Hermione's hand fly up to cover her mouth as she tried to supress her laughter. In front of her now was a bouncing, silver ferret.

Draco lowered his wand and gave her a reproachful look.

"You promised!"

"I'm sorry," Hermione said, giggling. "But you have to be able to see the humor in it! It is kind of funny, don't you think?"

"Hermione please," Draco complained.

"Alright alright," Hermione agreed, managing to calm down. "But tell me what was the memory that you used?"

Now Draco's lips curled into a smile.

"When I saw the test you left by the sink this morning."

A little thing I did for my Tumblr blog. My name is Shamelesscaptainswanshipper if you want to follow me on there, though my blog is mainly about Once Upon A Time.
Now I know that this scenario is highly unlikely for various reasons: Draco's patronus most likely wouldn't be a ferret because I'm guessing he doesn't associate ferrets with anything good, which is what patronuses are made of, good memories and him being turned into a ferret is definitely not one of them but it'd be pretty funny if it was!