I saw that too - didn't know what a castor was.

So, I did the only thing I knew. I searched "Google". This is what I came up with: "The beaver Castor canadensis is the largest rodent in North America and the largest rodent in the world except for the capybara of South America. An adult weighs from 16 to 32 kg and, including its 30-cm tail, a large beaver may measure 1.3 m long. Its ancestors were even larger."

Joanie, castor is the French, Spanish and Portugese word for beaver. So it's possible that the designs of castors that you downloaded were digitised by someone from one of those countries. Hugs and a flower sweetie.