Internal observation performed by oneself. Observations of the activities of the organs and their interrelationship. Of course anyone can do physiological anatomy. Anyone can dissect a corpse. But internal observation isn’t something everyone can do. Those who don’t have a certain degree of self-cultivation who haven’t reached a certain mental plane. Ordinary people can’t be so calm that they can see the working of their organs. Only a handful of people can accomplish this. AS for meridians you could never find meridians on a corpse. If you hope to find meridians on a corpse you’re looking in the wrong place. That doesn’t exist on a corpse. Nope, not at all. Meridians are a sort of channel through which the Qi and blood flow so it is a feeling of flow. Only in bodies are you able to locate meridians.