Find severing charm:
Go to the Herbology Greenhouse 3. Find the door thats 
guarded by Horklumps. Cast them with your Flipendo spell 
and when they are screaming - pick them up and throw them 
away. Now, go into the door, you will need to rid more 
Horklumps. When you are done-pick up the Severing Charm. 
Submitted by HopeWings