When Ron buys stink pellets from Fred and George, they set him a challenge.
Ron has to find 20 of these snake things on the walls and throw a stink pellet into them to turn them up the other way.
For every 5 you get Fred and George will give you a special Collectors Card.
The locations are as follows:
7th Floor
1. North Wing
2. Next to the Fat Ladies portrait
6th Floor
3. In Fred and George's bathroom
4. East Wing
5th Floor
5. Through the first door
4th Floor
6. Forth Floor Coridoor
7. Above Hospital Wing door
3rd Floor
8. Third Floor Coridoor
9. Defence Against the Dark Arts Classroom
2nd Floor
10. Secret Passagway
1st Floor
11. Hidden in a secret passage behind the Gregory the Smarmy statue
12. Transfiguration Classroom, climb the bookshelves on the left
13. Transfiguration Classroom, climb the bookshelves then walk around the ledge to the other side
Staircase
14. Between the Sixth and Seventh Floor, you have to stand closer to the seventh floor landing to get it
15. Above the Forth Floor Door
16. On the bottom Floor
Dungeon
17. Outside the Potions Classroom
18. Furthur down the same coridoor
19. Potions Classroom
20. Entrance Hall, nearest the Hufflepuff hourglass