Some horror stories could be due to poor hygiene in the preparation area. If the kitchen is dirty or the workers don't follow proper hygiene protocols, it can contaminate the chicken nuggets. There have been cases where people suspected that the nuggets were not cooked thoroughly, which is a major concern when it comes to food safety.
Well, some horror stories might be about finding strange things in the chicken nuggets. For example, people claim to have found pieces of plastic or other foreign objects. It's really off - putting.
There could be stories related to the quality of the chicken used. Maybe the chicken wasn't processed properly and led to some people getting sick after eating the nuggets. Also, some might have had bad experiences with the taste, like it being overly greasy or having a strange smell, which they considered a 'horror' in terms of food experience.