In Stoicism, one key aspect is the idea that all individuals have the capacity for moral and intellectual growth. The slave boy story could be related in that it shows that even a slave boy has the potential for such growth, which aligns with Stoic beliefs about the universality of human nature in terms of the ability to develop virtues.
One important lesson is about the universality of human capacity for reason. The slave boy story may illustrate that even a slave, who was generally considered inferior in ancient society, had the ability to engage in rational thinking. It challenges the common perception of that time and reminds us that all humans, regardless of their status, have the faculty of reason.
While it's possible for humans to contract dog mange, the risk is relatively low. It requires direct and prolonged exposure to an infested dog. However, people with weakened immune systems might be more susceptible.
I'd suggest checking out specialized graphic design forums. Sometimes designers share their own creations there. Another option is to search on Google Images and filter for the size and quality you need. Just be careful about the source and usage rights.