So, I've pasted in the HTML code for the GrammarCatz javascript here in a separate document, and I've reproduced yesterday's GrammarCat below so you can see how it works. For the actual commentary on the cat and an explanation of the English grammar, see the blog post: Grammar Cat #99: Monty Python Cat.
I'm sure there are much more elegant ways to do this, of course, but one of the great things about a teeny-tiny javascript like this that runs inside a blog post is that I just need for it to work. So, it shows the corrected cat and hides the corrected cat as the user requires, and that's all I need it to do! :-)
(Note that below I had to display the images at half the usual size so they would fit in the width of the post here; I have the post width set much wider at the GrammarCatz blog.)