Anatomy. Teaching from the chakras. Teaching from the muscular structure. Teaching from the energetic structure. Koshas and kriya and kundalini and karma yoga and bhakti yoga and “Oh good grief I’ll never remember all this!”
The first time you took a yoga class, did what the teacher was doing look all that complex? Did you have any clue? I mean, really, how hard could it be? “Step your foot back, relax, breathe.” Big whoop. Hundreds of hours of training for this?