The people who are most horrified that I spent about £2,000 on a hysterectomy for my guinea pig Ruby are usually dog owners who would spend 10 times that, if they could, on their dog. “Why didn’t you just get another one?” said a terrier owner I mentioned it to recently. “Would you just get another dog?” I asked. Most people are speciesist – it’s why we eat some animals but not others, and why many believe, in the pet hierarchy, the small ones are disposable. Anyway, Ruby was like a little dog. Even though it was 20 years ago, I can picture buying her (from an open-farm attraction with – my dream! – a guinea pig village) more clearly than the births of my children. She was scampering around, a flash of smooth, shiny brown fur, and looked so much less inscrutable than the other guinea pigs for sale; I’ve had several in my life, and she was by far the most intelligent and engaging. Ruby lived indoors, and I often let her run free throughout my flat in London. She came when called, and she could jump from the floor to the sofa, where she’d sit on me for ages and snooze. When I chatted to her, she would squeak back. I learned to open the fridge with silent stealth; otherwise she would shriek excitedly at the prospect of carrots or greens and stand up on her hind legs to be fed. She was family – when I went away, she and my other guinea pig, Puzzle (less tameable), would go to stay with my mum, who called them her grandpigs. When Ruby became withdrawn and no longer squeaked when the fridge door opened, the vet diagnosed ovarian cysts – not uncommon in female guinea pigs – but hers were big and she needed more investigations with a specialist, then an operation and months of follow-up treatment. The whole thing was sickeningly expensive, and I had to borrow the money, but I never once considered forgoing it, even though there were risks. I think, I hope, it was the right decision – she ended up living for another couple of years, until the age of eight, gradually less able to jump up on to the sofa but just as affectionate as ever. When I realised Ruby was probably dying, I stayed up with her all night. In the morning, I set her down for a few minutes to have a quick shower. I’m convinced she waited to say goodbye, because when I picked her up again she nestled into my neck for the last time and died, and my tears rolled down her glossy back. Those of us who knew her still talk about her now. So no, she wasn’t replaceable.