The 99% Invisible episode about numbers stations was interesting to me because radio is a unique form of communication as it relates to cryptography. Since radio is publicly broadcast, anyone can tune in, so while sending an encrypted message, you have to assume that your enemies are listening at all times. Because of this, using the radio to broadcast highly sensitive information such as important updates to spies in the field seems like an odd form of communication to choose. However, as was pointed out in the podcast, the benefit of using radio for communication is that it is accessible from anywhere, and it keeps the location of the recipient unknown, making it the perfect form of communication for spies who need to keep their heads down. This in addition to the use of one time pads which are in theory unbreakable without the key make numbers stations a surprisingly efficient way to distribute information.
In addition to the interesting content, there were a variety of techniques used to keep the podcast interesting to listen to. Even while people were talking, there was always background music, sometimes even a numbers station playing in the background. I would have thought that having someone listing numbers in the background would make it difficult to understand the podcast, but it was done in such a way that it actually made the audio more interesting to listen to, and it provided continuity between segments. In addition, even when there was dialogue going on, there was always something in the background to keep your ears fully engaged, and it strengthened the sense of continuity of the episode making it easier to listen to without zoning out.