Thanks for your interest, hopefully this answers your question. I haven't read the books for a while, so it may not be completely reliable.
If you have more questions, I think http://bartiforums.com would be more helpful. Jonathan Stroud answers questions there sometimes. This community's pretty dead, and I've closed my wiki account, hence the anonymous reply.
I think what the person above said is basically true. However, given that we've never seen any example of this actually happening within the series, I'd say it's a question that only Stroud could answer for sure, if he were so inclined.
My name is Ariana- I'm on the community development team over here at Wikia for the Book Wikis. I was checking out your awesome wiki and wanted to see if you were interested in a main page update- including a new skin, wordmark, headers, and a general reorganization of the main page. I could also add videos and more content.
Do you think you and the other admins would be open to that?
Let me know if you have any feedback, concerns, or suggestions!
That page is full of useful material but I think not all of it should be packed into one page, please try to copy and paste into the relevant pages or change the name of the article to something that makes more sense.
Yes, definitely needs to be sorted out. I'll try to do it at some point. It's a quick copy from a wikipedia page that was pointed, out, as it was deleted soon after. Probably crosses over with existing spell pages, List_Of_Magical_Objects, Demons, Magicians and List of Magicians amongst other things, which will also need a cleanup at some point.