Re: Ask sensei to demonstrate "at speed"?
The first time I tested my teacher was after I had been training for three months. I had a long history of studying "hard" arts and fighting sports. I always wondered why nobody who was serving as uke for sensei ever really tried to clock him. The cro-magnum part of my being decided to put that to the test when I was called up to serve uke for him. The attack was a shomenuchi. I launched myself into a full-hilt strike to his head. The next thing I was aware of was my flying into the air and into a padded wall. It felt like I had jumped off of a three story building onto a trampoline. Every ounce of force I applied to him came back at me in spades. As I was shaking the cobwebs out of my head I looked at him smiling at me saying "just go like this" [he went through the Ikkyo Irimi movement that he had so generously shared with me!]. I was hooked from that moment and am still trying to attain that level of execution of a technique.
Janet's comment is spot on. Just because we practice in a safe manner does not mean that it cannot work in a real life encounter.
A teacher is responsible for the safety of one's students. Insuring that lessons are learned and experienced in a safe manner is a minimum requirement in developing students of good character and skill. In all of my years training directly with my teacher (Imaizumi Sensei) I have never observed or heard of anyone becoming injured from him, regardless of the circumstance.