The thing that annoyed me about that is Medusa
was the name of one of the Gorgons. The Gorgons weren't Medusas. I'm sure Terry would have known that, but can't think why he put that in.
It's like when he put Pelléas and Mélisande
or Pelias and Melisande as they are called in Moving Pictures, when that is very much a Roundworld story. In Mort a Mellius and Gretelina are mentioned, who seem to have an identical story as the couple mentioned in Moving Pictures.
“Men never commit evil so fully and joyfully as when they do it for religious convictions.” – Blaise Pascal