Actually, Lecture 68 and 69 (with the associated comments) really helps clear it up more for me. It pays to read in order! [Scott's comment](https://forum.azimuthproject.org/discussion/comment/20453/#Comment_20453) was especially clarifying for the circuit metaphor (profunctors are machines that need an external energy source). Also Anindya's [proof of the snake equations](https://forum.azimuthproject.org/discussion/comment/20462/#Comment_20462) is a good companion to Dan's answer in this thread.