My cat is afraid of bos

Familiars CAN be physical animals, they aren't necessarily spirits all the time. And yes, it's also common that your familiar also happens to be your pet.

Wiccanery, they are not physical animals/pets. The end

You know you're all allowed to have different beliefs. Actually- it's apart of the guidelines for this forum! If wiccanery believes that a cat could be/become a familiar- respect that. Do not push your belief on to others. This is silly and disrespectful. Accept that they don't agree and move on.
And to Wiccanery's benefit, there other forms of witchcraft and religions that dictate that physical animals can be familiars, vessels, etc so even if yours does not, that's okay.