Why doesn’t this happen anywhere else? Cut your finger? Both hands get infected. Ingrown toe tail? Both feet hurt.
They have greatly restricted blood flow due to their structure, and very close proximity to the most important organ in the human body. And I wanna take a minute to appreciate how much of an evolutionary novelty sight must have been. Producing photo transferring chemicals and seeing your mate for the first time.
there are actually a few other cases of this in the body and it’s because your eyes aren’t actually a part of your bloodstream so the eyes are treated as foreign objects along withthe others I mentioned being thyroid follicles ovarian follicles and sperm inside testicular ducts the last 2 being they only have one set of chromosomes so are biologically different to you