This thread is straddling "things I fear in general that can possibly happen while at a zoo" and "things I fear that have specifically to do with a zoo" a lot. I don't say that to sound critical of it, I think it's interesting, but man, it feels silly to have expressed such a very first-world, privileged fear about maybe not seeing an animal while other people are discussing serious, life-threatening situations like mass shootings, physical altercations with angry visitors and dangerous animal escapes. These are very real and legitimate fears and risk of violence is a very frightening thing.
I'm going to throw out something new in the middle of both - I fear the killing of an animal, particularly by another member of its species, in front of visitors. Yes, those of us on zoochat are very, very well aware killing is part of nature, but I don't think it does well for zoos for visitors to observe that kind of aggression, especially keeping in mind the criticism some zoos have faced when visitors observe natural aggression between animals as if it is a consequence of captivity. I fear not only the effect but also bearing witness to it myself or being there on the day it takes place.