"This works" "this doesn't " is another , notice that usually when he says this , his posture does not change. What is is that he switches on / off without changing things overtly?
Watch his hips and his wrist very carefully. His posture does change. It's just so small that you might miss it unless you were looking at the right spot at the exact moment it happens...
Ikeda sensei is absolutely fascinating. Hopefully when I have trained much longer I will be able to describe what is going on in those exercises. They are among my favorite things to work on in the dojo.