Is the teacher learning?

I just listened to a captivating TED talk from a gentleman who voluntarily did not speak for 17 years. As one would imagine, he has some interesting things to say about listening. During his silence, he was a college professor where he would write and use a make-shift sign language to communicate. He said many times as he would make signs and gestures the students would play a kind of guessing game trying to make out what he was trying to say. Many times they got it right. Sometimes they would not. Frequently, he would think to himself, "That's not what I was trying to say!" And then he'd catch himself and think, "...but it probably should have been..." as he realized the students had struck upon a critical angle or point he was overlooking. His point was that if you are not learning while you're teaching, you're probably not really teaching.