He demonstrated a few commands: Rex found a fake pistol hidden in a backpack and even lay down next to a person who had a special marker in their pocket. The children clapped.

But suddenly, everything changed.

As the officer was about to finish the demonstration, Rex suddenly became sharply alert. His ears perked up, the hair on his neck stood on end. He froze, staring at the crowd of students. And then… he lunged forward with a growl.