While males seem more likely to show affection by licking me, and then me returning it by petting them (this has happened with about 4 males so far), females seem to like to bite me. Not like I'm food, or clamping down, or defensively, they just seem interested then use their teeth, and will gradually try and nibble harder if i dont discourage them ("Ow, that's my finger" then I push them lightly back because of it (and when I say lightly I dont mean "whats light to you could be a shove to the rat" I mean lightly, like enough for them to move back on their own and me using less force than petting)). But it seems like the females never learn and never lick.

I dont blame them for it since they arent trying to eat me, arent trying to hurt me, and from the way it feels arent trying to even be defensive, they just seem curious.