Car is one of those repurposed words. It used to mean any wheeled vehicle until around 170 years or so ago. Automobile was used at first for cars. When I was young automobile or auto was the preferred term. Car or auto can be used for motorcycles or trains, there are just better words for those.
Human sexuality is a spectrum and not an either/or situation, and should be treated as such. That being said, a chromosome test would answer the question in over 95% of cases, I believe. I could be wrong about this, so anyone with a better understanding, please correct me.
Could also be bone eating bacteria.