I could never understand why there's a lot of nekomimi fanart of Yuki.

It's something about how she just stares at you blankly, like a cat does.
...that, and it's cute.

The weird thing is that she's more the size of a rat here.

Nah, her size here is about right for a cat. Where do you live that the head of a rat is as big as your palm?!

I'm looking at the length of the body, not the size of the head.

All I got to say is: if you got rats that big runnin' around you best get out of there. I mean, get up right now and run, cuz' you livin' next to some heavy radiation and you 'bout to start growin' eyeballs on your ass.

Don't worry, I don't have rats. The weird thing is that when I compare Nagato with the hand, instead of Nagato looking bigger, the hand looks smaller. It looks smaller than a normal human's hand. There's no other reference in the picture, and yet both the hand and Nagato look smaller than they should be. :/

GordonFreeman said:
All I got to say is: if you got rats that big runnin' around ... you livin' next to some heavy radiation and you 'bout to start growin' eyeballs on your ass.

Not neccessarily, see [http://en.wikipedia.org/wiki/Bandicota_bengalensis] those rats get up to almost half a meter long and have been known to attack babies.