What EXACTLY is the feeling that you have to call yourself Otherskin?

I mean, I honestly don't get it. What I've read is that you think you're connected to the spirit of an animal. Or something? But how does that manifest itself? I mean, you're on the internet, eating human food, dressing like humans, etc. What exactly makes an Otherskin? Isn't it perhaps more likely that these…

What would you do if a stranger approached you and told you that you didn't exist?

Imagine you're just walking through town, everything going perfectly normal. Suddenly, someone approaches you and explains that you don't exist. They justify it in such a blatant way, using complicated scientific facts and theories, that it actually makes sense. Then the person leaves, and you never see them again.