Like a lot of beloved movies, Zootopia was once a very different beast. For one, the story wasn't always centered around the journey of Judy Hopps, ZPD's first bunny cop. Initially, Nick Wilde the fox stood center stage. It was late in the game when producers decided to turn the focus to Judy, believing her optimistic outlook was the right way to introduce the bright and prosperous Zootopia. But Nick's wry pessimism would have been a perfect fit for the dark original vision of the city.
Take a look at that concept art above, on the right. Anything stick out? Yes, Nick looks predictably dashing in a suit, but he's also got a special gadget around his neck. That's a shock collar. The idea being if he ever got too out of line, a shock would emnate from said collar, bringing him to heel.
Nick doesn't have to wear one of these just because he's a shady guy. In the preliminary drafts of the movie, every single predator in Zootopia was required to have a "tame collar" strapped to their necks at all times. Meaning that even softies like Clawhauser were publicly marked as potential threats.
As the producers explain, this was supposed to be how predators and prey started their uneasy truce. That's in stark contrast to the final version of the movie, where even kids know that animals evolved beyond the "primitive, savage ways" and learned to get along with each other simply because their compassion grew along with their intelligence. As the creators tell it, the shock collars weren't really necessary for the safety of the prey, but the fascistic tactics "made them feel better" -- and isn't that the most important thing?