On Saturday morning I cupped a grey mouse in my hands. He was still warm and breathing. It was just a mouse, a creature routinely dismissed as a pest or a cartoon character. But looking at him, feeling him in my hand, I felt a profound sadness.
Last week I pointed to a dramatic decline in the number of domestic dogs and cats in Australia. Twenty years ago, there were 7 million. If the same ratio existed today, with the human population one third larger, there would be 9.3 million domestic dogs and cats. But there are only about 5.75 million. 
Among the hundreds of comments on the column were some that took me to task for saying domestic cats are largely innocent of the carnage that feral cats have inflicted on native wildlife. It's true. There are, by rough estimate, about 15 million feral cats in Australia. There are about 2.5 million domestic cats, and about two-thirds of these are house cats. So feral cats do more than 90 per cent of the killing.
But domestic cats are part of the problem. That's why, a year ago, when a neighbour's handsome little cat started visiting our house each day, I ignored him for a month. We did not feed him for four months. But he kept coming, staying longer and longer. He is now a member of the household.
I've never seen him try to kill anything but, within days of writing last week's column, I got a comeuppance.
Last Friday night I heard small squeals coming from the dining room. To my shock, a mouse ran across the floor, chased by the cat. It hid behind a pot. All I could see were its tail and a tiny paw.
As happens, when confronted with the unexpected, my first reaction was immobility. By the time I intervened in the cat's repeated catch and release, the mouse was so exhausted I was able to simply pick it up. I took it to the far back corner of the back fence and dropped it over. This was near the neighbour's tool shed and compost pile, where they had told me that rats or mice had taken up residence. I thought I'd given the mouse a chance.
On Saturday morning, I found the cat looking under the couch in the dining room. To my alarm, I saw the mouse was back. It had been harassed all night. When I retrieved it gently from under the couch, it lay limp in my hand, alive but spent.
Worse was to come. On Saturday night, we found the cat chasing another mouse in the dining room. Again, catch and release, with squeaks of terror. The second mouse also hid under the couch. When I when to retrieve it, I found it huddled against another mouse. It had lain down to die against its nest-mate.
When I put them in a box, the surviving mouse hid its face in a corner. It had given up.
I took the box to a hole in the fence next to the mice habitat down around the shed. I was encouraged that it walked away towards the shed. It was too exhausted to hurry. I hoped it would survive the ordeal. I buried its nest-mate in the morning.
After our cat's first experience with hunting mice - the job it was born to do - it became more furtive.
The next morning, instead of the usual nestling on the bed before breakfast, it gave croaking wails, demanding to be fed. It wanted no part of the bed ritual. (After I took numerous measures - he's locked in at night and wears a bell - to inhibit mouse hunting, he has returned to his normal affections.)
The journey from domestic cat to feral cat can be short.
The toll feral cats take on marsupials, birds and reptiles is staggering. One frequently mentioned estimate is 70 million creatures killed by cats every day. Per day, not per year.
Every night, millions of small marsupials squeal in terror, unheard and unsaved, destroyed by useless, destructive predators that are a by-product of our gross mismanagement of the environment, which was far healthier before the advent of European settlement.
The prolonged suffering of the mice in my home hit me. As I held that first mouse in my hand, the one I could have saved, he gave one last sigh and died. I buried him in the back garden, with a heavy heart.
Twitter: Paul_Sheehan_