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.

The dose makes the poison.

"Hey try this candy."

looks inside candy; dog poison

Every substance has an LD50.

a small bottle of aspirin can kill you.

Theophrastus Bombast von Hohenheim, "Sola dosis facit venenum", only the dose makes the poison.

There’s a pretty silly plot point about “blood thinners” in an old flash-based detective series, Nick Bounty.

Nick works out that a dame has been poisoning the town, and goes to confront her. She shoots him. He has no vest, but somehow he’s not bleeding. Nick admits that he realized he’s been taking the poison unknowingly during his investigation, and so his pulse had already been grinding to a standstill, hence no bleeding. He figured his best chance was to delay the culprit until reinforcements came.

Then, paramedics come and easily revive him thanks to no real blood loss.