The bad thing is that people in urban neighborhoods use rat poisoning. In one of the parks here in San Francisco, an owl was found dead due to having eaten poisoned rats. The necropsy showed that the poison had infiltrated his entire body. I’ve seen dead rats lying around, bleeding from the mouth or hemorrhaging through the skin — these are signs of rat poisoning. And I’ve seen rats in such pain that they can barely walk. The poisoned rats are easy prey since they move so slowly. They become easy food for raptors and other animals, including coyotes — and up the food chain go the poisons.
Most all rodent eating animals are carrying rodenticide poison loads. An overload can cause lethargy and other debilitating conditions. If you see a coyote that fits this description, please call Animal Care and Control — there are treatments for rodenticide poisoning.