The first time was when I was getting them into Standing Head to Knee. I showed them how to lock their knee.
"You push the knee back and THEN pull up on your quadriceps muscle. See how it pops up and away from my knee? This is a locked knee. Beware, it will unlock on you. So you must re-engage it in the posture."
Looking at the dialogue, it doesn't say this. But this is how you lock the knee. And I had two students thank me afterwards for showing them this... Because they didn't realize you had to do more than push the knee back to lock it out.
The second instance of me having to show them how to do a posture came yesterday during Triangle pose. The first set of Triangle was rough. Students not sitting low enough... Then when they went to rotate their arms, they were bending down to get their fingertips in between the big toe and second toe.
This is wrong. So I showed them in between the sets (which also gave them a nice break.)
"You sit all the way down, making an upside-down L with your right leg," I showed them. "This gets you down into the hip flexor. Knee should not go past your toes. If it is, move the straight leg out more, making a wider gap."
"Then, you windmill the arms," I showed them. "You move them at the same time. JUST move the arms. You do not bend your torso down."
"Then, you sit lower, stretching your right arm down in between the two toes and stretching your left arm up. You don't bend the torso. When you bend down, you lose the triangle gap that is created. And that gap is why the posture is called 'Triangle.'"
"The two arms should be on top of each other, stretching in opposite directions," I went on. "The two shoulders are stretching apart. You are twisting your torso back at the same time."
In the second set of the posture, there was noticeable improvement. And I had a number of students thank me after class for showing them that.
"I had no idea!" was the general sentiment.
The dialogue is great, and certainly the best tool in our arsenal. But sometimes you have to actually show them, in addition to relying on the dialogue. If you only recite dialogue, your students aren't necessarily going to grow. Some people are visual. And you can't always see how to properly do it in the classroom.
Also, I'm sorry... But Triangle is one of my favorite postures. And it makes me sad when people do it wrong because they've never been shown how to do it.