I’d say AeT running feels like quiet nose breathing. It should feel easy and you should be able to talk in full sentences. If your nose breathing feels forced, you likely have passed your AeT into your zone 3. The aerobic threshold isn’t exactly rocket science but all of use sure do feel the need to try to pinpoint an already somewhat arbitrary value. I think the real value of the AeT is in simply slowing down, humbling ourselves and enjoying running.