First of all, this has been rather entertaining to read.
Secondly, given the current discussion you might find this interesting.
Some species of Whiptail Lizards are made up entirely of females, and they reproduce by parthenogenesis. Parthenogenesis is the development of an embryo without fertilization from a male. Even though they can reproduce without males the females will mount others females and act out mating. This stimulates the female and increases her chances of reproducing.
So I dunno, as odd as it sounds, perhaps the reason girl ratties will mount eachother is similar to why Whiptail Lizards mount eachother.
Secondly, given the current discussion you might find this interesting.
Some species of Whiptail Lizards are made up entirely of females, and they reproduce by parthenogenesis. Parthenogenesis is the development of an embryo without fertilization from a male. Even though they can reproduce without males the females will mount others females and act out mating. This stimulates the female and increases her chances of reproducing.
So I dunno, as odd as it sounds, perhaps the reason girl ratties will mount eachother is similar to why Whiptail Lizards mount eachother.