Alternative Imgur version
Today used as blood thinner, Warfarin’s first commercial use was rat poison.
Yes, this may seem scary, but it actually makes sense. The blood thinner makes a rats blood so thin that it kind of just seeps out of their veins without any damage, causing delayed and heavy internal bleeding leading to death, but a human with 100 times the body mass is completely fine.
This may seem cruel, but it is kind of necessarybecause rats are too smart for other methods or poison: if a rat notices another rat dying shortly after eating from a food source, it cab make the connection that the food is bad and will no longer eat from it, so you need something with a lot of delay to ensure all the rats have eaten the poisoned bait before the first one dies.
I don’t agree that ‘rat poison is necessary’. That would mean by extension that it’s necessary to kill all the owls and birds that feed on poisoned rats - a real and current problem due to overuse of rat poison.
There are other effective means of rat control - poisoning is just the cheapest and easiest.