900. Deon was upset with Ezra. Ezra had left a puddle of water on the bathroom floor after taking a shower. Deon started yelling, "How many times have I told you to mop up all the—?" He went silent. He walked away and sat down on the sofa. Ezra knew why his dad had walked away just as he was getting warmed up. It was the anger sensor. A year ago an inventor, Thomas Alva, had gotten angry about all the anger in the world. Anger causes more pain and sorrow than all the diseases put together, he thought. He invented an anger sensor that was embedded in satellites blanketing Earth. Detecting anger, the sensor replaced it by beaming beautiful music to the individual. Ezra, who had to walk to and from school past growls and barks, emailed Thomas. "Your sensor works great on dads. Can you make one for dogs?" 5.4