Hatching #124 (Fandom)

This week's newly hatched plot bunny-
Week: Week #124 (Fandom)
Plot Bunny Idea: Write about a virus that spreads through Hogwarts infecting the Slytherins (Severus Snape, Lucius Malfoy, etc.) and the Gryffindors (James Potter, Sirius Black, etc.). However, this is no ordinary virus. This was created as a prank (can be done by the Gryffindors or the Slytherins) and works on the victims, then backfires on the creators somehow. Write how and why the prank was created, its execution, and then how the virus switches back and forth, striking the Gryffindors and Slytherins.
Fandom: Harry Potter
Special Limitations: None
Comments/Other: I wrote this more for MWPP, but making it for Harry Potter's generation is fine too. Write as much as possible, and enjoy. By the way, this was inspired by a previous bunny and a story from the Winter Challenge's Archive.
Creator: Lady_Gallatea_Ravenclaw
Date Bunny was submitted: 7/24/2005
Date Bunny was issued: 7/26/2006

Feel free to get inspired and write a fic based on this bunny!
If you have any questions, wish to know more, or have a plot bunny to submit, please visit:
http://sfarchive.beastlet.com/WeeklyHatching/