According to current best practices a RESTful URL for a given thread on a message board should look something like this:
http://domain/forum/threads/3
It is also a common SEO practice that URLs should contain keywords (slug), so perhaps the above URL could become:
http://domain/forum/threads/3/title-of-this-particular-thread
Now, to edit this thread, again, according to the guidelines I've linked to in the first paragraph, the URL would be:
http://domain/forum/threads/3/edit
What should happen when someone starts a thread with the title of "edit"? How should it be decided if the thread is to be shown or edited?