I mentioned this instructional film in yesterday's post devoted to Shallow Grave at the Central Cinema, where it's the curtain-raising attraction.

But it's also in the public domain, so I'm going to showcase it here, too, because I can't stop thinking about it. It's so...long, and weird, and unclear, and it features the most amazing lesson about going swimming too soon after eating a hot dog you'll ever see.

Thanks to Slog commenter G.