Tbh, I’m not sure what made me come up with the name Castor at the time xD
Usually, I spend ages thinking of suitable names, and often my characters are named for pretty specific reasons with meanings behind the names or their names representing things, but with Castor and Castoria, it was just one of those weird ones where for some reason, I had it in my head without looking at anything and just rolled with it xD
Some people have since told me that Castor means some pretty funny things in other languages, haha. That would be pretty cool though if it happens to be a toxic plant though cos, as you say, it would be quite suitable :D