What is a potential sign of an unhealthy animal related to social behavior?

A potential sign of an unhealthy animal related to social behavior is not socializing with other animals. Social behavior is crucial for many species as it can impact an animal's mental health and overall well-being. When an animal typically known to socialize chooses to isolate itself, it may indicate stress, illness, or discomfort. This withdrawal can be a sign that the animal is not feeling well, either physically or psychologically.

In contrast, increased vocalization can sometimes be a normal behavior, particularly in certain contexts, and does not necessarily indicate illness. Aggressive interactions are often part of natural behavioral dynamics and can occur for various reasons, including territorial disputes or mating behaviors, but they do not directly indicate that an animal is unhealthy. Playing actively is generally a sign of health, as it indicates that the animal is energetic, engaged, and in good condition. Therefore, the behavior of not socializing is more clearly linked to potential health issues, making it the correct answer.