YouTube Embed widget
Sorry: is the wiki embed something cIRcle governs? I'm not seeing the link between my question and cIRcle.
The page in question was http://wiki.ubc.ca/Documentation:Annotated_Presentations/DIY_Media, which was embedded on http://diy.open.ubc.ca/annotated-presentations/. Without the paragraph above the YouTube video under the 'what are annotated presentations' header, the accordions didn't display.
Then, again, there was a problem with a YouTube video: one of the ones linked on the page was made private. This broke the accordions, too. I'm not really looking for a fix, although it would be nice if the plugin was made a bit more tolerant of issues with videos, as much as I'm looking to make sure other people know what to do if their pages break: that is, check your YouTube videos first.