After having wanted one since I was a kid (my mom can’t stand the look of their tails, so she prohibited it :rolleyes: ) I finally got 2 rats yesterday. I had hamsters when I was a kid and I find so far that the only real difference is the rats are much more intelligent. One of them, Bettina, did something today that I wasn’t sure of. Yesterday I offered her the back of my hand to sniff through the cage, handed her treats, etc. and she seemed totally fearless. When I came home today she actually ran up to me and looked excited to see me, so I decided to try something and opened the door and stuck my fist in. Right away she ran up to me and sniffed my hand all over . Then she opened her mouth just a little, slowly and kind of hesitantly, and I felt her teeth touch me a little. I pulled away quick and that scared her, and she went and hid. I’m not sure if she was trying to bite me or not. She sure didn’t seem agressive at all. Do rats nibble just to check you out? When I had hamsters, they bit very quickly and without hesitation, and this doesn’t seem like the way she was acting. Rat owners, what do you think? I want to make sure I’m fairly safe before I try to pet her (based on how bad hamster bites hurt, I’m sure rat bites are much worse).
Maybe she was waiting to take treats by hand and you confused her by not having any. So she tasted you. 
My guinea pig does that. She also licks my fingers. I think she thinks I have carrot fingers. shrugs Maybe your rat is checking your hand for food? Or maybe she is just seeing who you are, so she can remember you are somethin.
Our ratties are friendly, affectionate and yes, occasionally they nibble on us, much as you described - not a quick, scared or aggressive kind of bite, but more a tentative, “I wonder what this guy tastes like” kind of semi-bite. Encourage Bettina to get used to your hand, but just be ready to move again if she tries to bite. Rats are pretty smart, and she will get the message.
Oh, also, any rat may bite if they mistake you for a treat. Mine will eagerly devour Yogies from my hand, but every now and then after they’ve taken the Yogie, they come back and take a chomp out of one of my fingernails. At least they always look sorry.
We had a pet rat that nibbled fingers too. She never bit hard enough to cause any pain, but would gently gnaw on a finger now and then. I have no idea why she did it.
Rats are fun little critters. Ours did nibble occasionally but never broke skin. Once they get used to you, they can actually be out of the cage quite a lot. We’d let ours run around the living room, up on the bed, under the covers. They loved to play hide and find.
An important thing for male rat owners to learn is to never let the rat under the covers of the bed with you when you are only wearing loose boxer shorts. 10 years later and my wife still teases me about how hairy grapes are a healthy part of a rat’s diet. That was the only time I yelped and pulled back quickly from one of the rat’s little nibbles. She didn’t need to get to know me that well!
Sadly, rats live such short lives. 1-1/2 to 2 years usually. Too sad for me. And your ratless friends never understand why you spend $70 for cancer surgery on a rat that cost you $4.
<crossing fingers very tightly>
Milo and Rodney are two years old next week. Neither has ever been to the vet, but they both seem happy, healthy and active. And I have met a four-year-old rat, so I remain hopeful.
Be sure to wash your hands after preparing food if you’re going to handle rats. They pick up information about their world by mainly by smell (as opposed to sight) and if they smell food on your hands they may not know where fingers end and food begins. I owned rats as a teenager and there were a few problems with the rats getting excited and snapping at someone’s hand because the person smelled of food.
you can actually teach them not to do that, by blowing gently (very gently) at them when they go to nibble - it doesn’t hurt or scare them, but it makes them realize that they can’t do that.
Really, they are just like babies in that they taste things to figure out what they are. My gerbils did the same thing, not at all agressive, just curious.