It's very curious that Alexa shuts up for that specific question. It's not like the technology has difficulty understanding the person speaking, that much was demonstrated by the previous 2 questions. After the news about the CIA being able to use smart TVs to spy on people, this behaviour by Alexa is enough to make one a little paranoid.
I originally saw a version of this video thanks to Alex Girard, but that one is now dead due to a copyright complaint. I suppose this video may not last long either, so watch it while you can.