Several young boys were reaching precariously over the railing in front of the lion cages and teasing the cats. By balancing on the railing and stretching their arms the boys could just get their hands close enough to the cage front to be dangerous. A keeper, seeing what was going, on decided to teach them a lesson.
This particular keeper was big and burly, and had a gruff, deep voice to match. He managed to sneak up behind the boys without their noticing, and the next time they reached out to the lions, he bent over them and let loose with a deafening roar.
The kids were so startled that they lost their grips on the railing and crashed to the ground.