Re: If you're looking for a challenge...
One of his sidelines was selling catgut and ratgut strings
I'm willing to be corrected but I suspect he was having you on. So-called catgut instrument strings are made from much larger animals' intestines.
A cat's might be long enough for a small musical instrument but I doubt a rat's would be.
And it's quite an involved, time-consuming process - you don't just strip them out and wind them on.