As it happens most of my "aha!" code-related moments come when I'm either under the shower or when I'm washing the dishes. Very rarely did it happen for me to look at a piece code while in front of my computer and then immediately be stuck by what that code does or by some hidden bugs in it. It's all sort of mechanical, at least while I'm sitting at my desk. I'd say it would be very hard for people like me to reproduce that "aha!" moment during an interview, in front of some other people who expect me to have those moments of enlightenment right there and at that precise moment.