A few years back we had a rat problem. Someone had left a bag of rice at ground level and one of them found it, so for the next several months they prowled the house for any available foodstuffs. My housemates and I were never very clean at the best of times, so even if we took efforts to lock our food away, they could always find crumbs.
So we set traps. We stomped and shouted. We tried various forms of bait. We proudly counted kills, thought of new places to set the traps. We tried new tricks. We looked things up online. And, quietly, we wondered if we'd have to move out, or hire an exterminator. Neither sounded appealing.
The internet told us that the key trick was to make sure there was nowhere the rats could get in, and in an old house like ours, with a basement that floods whenever it rains and too many windows, that seemed an impossible task. "You'll never kill them all," the internet promised. "If you've seen one, you've already got a whole colony." "You are fucked."
The quick and easy solution was always poison, but the internet warned us against that, too. They die slowly with poison. They wander off to their hiding places and die in the walls, and then you'll have the rotting corpse to deal with, until the flies pick it clean. So we tried to think of other solutions: can we borrow a cat? Can we try one of those anti-rat noisemaker devices that studies show don't actually work that well?
Another corpse for the pile: the trap worked, but it had killed a few before, so the rat got out and crawled across the room and died in a puddle of blood on the floor where I usually sit. Cleaning the blood off hardwood floors is harder than you'd think, and by the time I was done the room stank of rubbing alcohol.
I couldn't invite people over, and with every rat sighting I came to dread being home more and more. The rats were all I could think about. I'd check the traps, not so I could reset them, but so I could have the satisfaction of seeing that we'd killed another of them.
We never did find out why they disappeared. Maybe their food sources finally dried up. Maybe the neighbor's cat finally got them. I doubt we killed them all, though. It doesn't work like that.
