I had a snake come out of the wall behind our toilet through the hole where the water line was. My husband didn’t believe me. Fortunately it was just slithering back through the same hole when he went in to check. I never went into that bathroom again without the light being on first.
A buddy of mine lost his large boa in an old house (1890’s) that had been divided into four apartments. He would visit a friend over the years, and said that people still caught glimpses of the snake now and then those many years later.
I imagine with the remodeling there were lots of spaces behind the walls, and lots of mice.