1 Monty: Whatever possessed a Pope to install dangerous traps inside the Vatican itself?
2 Minnesota Jones: Oh, it wasn't the Pope. In da Vinci's time, the church was pretty much ruled by the insinuative influence of one Cardinal Cascabel.
3 Minnesota Jones: His rogue interpretation of scripture led to inquisitions, torturings, and murders across all Christendom.
4 Monty: Wow, sounds like a nutcase.
4 Minnesota Jones: Yes, he was a loose canon.

I completely didn't expect this, but there is indeed a Wikipedia article on loose cannons. Not to be confused with canons of course, loose or not.

And here I was wondering what I could possibly write in this annotation. Now it's all done for me!

Now I just have to sit back and wait for someone to say:

"Lose" only has one "o"! It should be a "lose cannon"!

EDIT: Wikipedia has made a liar out of my by deleting the article on "loose cannon". The page now merely contains a redirect to the Wiktionary definition.

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2018-02-04 Rerun commentary: Wikipedia, in its infinite wisdom, has turned the tables and made me a liar again, by reinstating the Wikipedia page for "loose cannon". According to the page's edit history, it was recreated in 2009, over 2 years after this comic was originally published. In the 8 and a bit years since, it's grown to a massive 37 words of description, plus a list of books, songs, and films titles "Loose Cannon".

There is, by the way, a stealth pun in this strip, if anyone is interested in trying to find it.