Don't forget the rats in Guards! Guards! as well.
And all the rats in Feet of Clay - they play quite an important role.
I think Terry is fascinated by rats and how they've become sort of attached to humanity. There's a saying about how you in a city you are never very far from a rat. And we've got a culture that vilifies rats as being dirty and spreading disease. Even the word 'rat' has become very negative. If you call someone a rat, you usually mean it in a negative way.
And yet, anyone who has ever had a rat as a pet will talk of intelligent, friendly and very clean animals.
I can imagine Terry being interested in this apparent contradiction.
I don't know if he's ever had pet rats, but I do remember that he did a lot of research on them when he was writing Amazing Maurice - I don't have the book to hand, but I think there's an author's note about it in the book.
Terry is a cat person. He has loads of cats living at his home, so I suspect he doesn't come across too many rats - unless they are gifts from his cats.
Look, you've got it all wrong! You don't NEED to follow ME, You don't NEED to follow ANYBODY! You've got to think for your selves! You're ALL individuals!
Yes! We're all individuals!