Of my six, I have one who used to bite hard enough to make me bleed and he'd never been handled before in his life and was terrified of me. With a lot of handling, he hasn't bitten me in months now (knock on wood).
Yes, they recognize their owners (by smell). But they have to learn you first, which may take a while.
Just want to add a note that most probably know but I just found out! Rats can carry tetanus (as many other animals can), so be sure you have your tetanus shot. I have to go get mine soon, I know it's been over 10 years since I've had one.
But back on topic, I don't think most rats want to bite, like hippy said. They'd rather run, hide, eep, etc. I'm sure as a last resort to protecting themselves, or out of confusion they might bite, and I wouldn't put anything past a wild rat (or cat, dog, or anything truely wild) though.
My boys 'play bite' sometimes when we hand wrestle. It usually consists of them grabbing my fingers with their teeth and attempting to pull my hand deep deep into their cage for more play. If they EVER get too rough with me I just make my own EEP noise and they let go right away.
Mine play bite, rarely very hard. Though, that's with me. My little bro put his lips to the bars for a *kissy* the other day and Toby bit him hard and drew blood but I think he had just eaten something. Plus, I still haven't quite gotten out of the habit of feeding through the bars. I do it when I'm eating something and give them a piece of it, but too busy to handle them.
I have previously been bitten twice by rats in pet shops, enough to make me bleed, but it didnt hurt to be really honest, its mostly shock. That of course was my own fault for being young and sticking my finger in the cage when there was a sign saying not too haha.
Out of the 9 rats i have owned in the past including my 4 boys now, none have bitten me, not even in play fighting, but i had to re-home 3 girls and apparently since they left me they have all gotten vicious but i do blame that on them not being handled as much as they should be.
Billy, one of the the bucks i own at the moment has bitten my little sister more than once, and nobody else will put thier hands in his cage. I think he recognises me as he lets me maul him and gives me little kisses ^_^
i think really as long as you handle your rat as much as possible s/he will be fine
I have been bitten a few times now. BUT I take in some pretty hardcore rescues. I was bitten yesterday having to hold my half-wild boy for gassing. He was very ill and was about to be suffering. He got sooo frightened and panicked and bit me. It was startling but not really painful. I just ignored it and kept holding and patting him, and telling him to let go.
I had 7 of these half-wild rats and they are the ones who have done the most damage....hehe. My domestics I have been bitten a few times mostly because of sticking my hand in between 2 rats or grabbing a rat that had decided my vicious old girl was friendly and she was about to grab a paw and try to bite it. The grabbed (but now safe) rat is startled and thinks I am the other rat trying to hurt them. I figure my hand can take the bite a whole lot better than a tiny rat body.
On that note, if you have nice domestic rats that you treat gently, don't startle out of sleep until you know them better, don't feed thru cage bars, etc...you should never ever be bitten.
When I first got Nyah, she sunk her teeth into my index finger when I stuck my hand in the cage to swap out the food bowl. It was the first week i had her, and she hasn't bit me hard since (a couple "warning" nips, but nothing like that first time; she was in my finger all the way up to her gums.)
Ruby just did something similar. I was standing in the playpen barefoot cleaning their cage when Ruby sunk her teeth into my big toe (no provocation; she just walked over, and went gums deep.) She's extremely timid and has not been handled much at all (only been the second week owning her though.)
She also bit me on the "meat" of my palm a few days ago, when I presented my hand to her so she could sniff it and figure out it wasn't edible. She sniffed it, and bit it slowly (the same way most rats will give a gentle little nibble, except she bit a little harder.) Enough to draw blood, but not terribly painful.
Basically you'll have to initially endure several weeks of potential hostility while the rat becomes accustomed to you. After that, they should warm up to you, and you shouldn't acquire any new scars (from their teeth anyway; Nyah has adopted the practice of trying to climb up my bare, hairy legs, leaving my calves looking like a cat's scratching post.)