When you have finish the game don't talk to the head master to count up the house point's. Go to Fred and George's shop and they will sell a spellbook.

PS. I think you will need 50 beans.

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

To find the secret passage just go out into the 7th corridor.

It is the big book shelf use ron to open it.

It will take you down to the 4th floor.

PS this is great for getting past prefects.

When you are trying to save nevele from the ghoul.

You will encounter 3 hinkypunks use ron to get them in a corner, use lumos duo keep using it until there visible then use flipendo.

Twice on each one.

Then 4 will come out and you have to do the same again.

Go through a few doors and you will encounter a toy robot to beat it
when it shoots missiles at you quickly use flipendo when it shoots at you.

After you beat the robot use lumos duo on the crystal ball then you have to face the ghoul, beat the ghoul shine lumos duo make sure you get it in the cage.

Hope it helps.