To eat rats? Or to get shooting practice?
On some level there is a instinctual human drive to kill rats:
https://www.youtube.com/watch?v=PXTiYQzzbB8
Having it I would guess it dates back to the middle ages and the black death, or.....it relates to the danger that rats display to young children. So if you have young kids and you see a rat, there is a danger there, they will chomp on them if hungry.
In any case though I would cheerfully kill any and all rats and feel quite fine doing so. I have not had to do so though, but find this aspect of atavistic behavior rather interesting.