If you want to tell Kodak to cut your Kodachrome film into strips instead of putting the slides into little plastic mounts you have to snip the corner off the processing envelope at the dotted line. This is not explained on the packaging (or anywhere else, for that matter).
The only way to find this out is to ask Kodak. Once you know how to communicate your instructions you’ll never need to ask again – you’ll just know – and nobody who isn’t already in the know will be confused. I’m sure this is the only example I’ve ever seen of a secret code used in customer communications. Can you think of any others?
Incidentally, the only place in the world where beautiful Kodachrome slide (and Super-8) film is still processed is Kodak’s lab in Lausanne in Switzerland.