I posted the tale on one of the other bestiality threads, but I'll give the short version here; I was living with a boyfriend just out of high school,, and he had a rottweiler. I told him the dog was a hard limit, and we agreed. Then one night he brought a number of friends over and asked me to do it with his dog in front of them, and i refused, which earned me a whipping in the backyard at night. He ignored my safeword, ignored my handsignals, and didn't stop until he and all his friends had a go at me. Then he cut me down, pissedon me as I lay in the dirt, hogtied me, and put me in the doghouse in his yard all night. Next morning a bee stung me, and I went into anaphylactic shock. His little brother came by, saw me in trouble, and called an ambulance.
Now the details:
He started drinking before his friends walked in. By the time they were all seated and watching the football game, he was soused. when I came in with another beer for his best friend, they were bored because their team was losing and looking for something else to do. They saw the dog, and told me to strip and lie next to him. His nose went straight to my crotch; he always did that. Then he started licking.
I was horrified, but the guys thought it was funny. They laughed, and my boyfriend told me he wanted me to let the dog fuck me. I said no. he insisted. I refused again. He slapped me and told me to do as i was told by my master.
He was really drunk by then, and I don't like him when he's drunk. I went down like he told me to, and his dog came up behind me. He started licking, which I'll admit I did enjoy; my boyfriend didn't like eating me out, and I missed it. Then the dog got aroused.
He put his paws on either side of my body, and between my legs I saw the foreskin roll back and his cock came out. It looked like a pink hot dog; I didn't see any knots like they describe in the stories. It was pretty smooth, kind of a reddish-pink color, and sort of coming to a gently-rounded point at the tip. his size was about equal to a hot dog, too; it wasn't really big. I mean, a girl is built to take a human male's cock in her pussy, and a dog is smaller than the avaerage human male, and correspondingly, his equipment is smaller too. I held still for a moment, kind of frozen; I didn't really expect he was actually going to know what my boyfriend wanted him to do. While I was frozen, he pushed himself in me. He wasn't really big, or wide, and it wasn't really painful. It felt as though my boyfriend had pushed his thumb in me, which he'd done several times. But all of a sudden the thought just made me sick; I lunged forward and got out from under the dog, grabbed for my clothes, and started yelling at my boyfriend. He got pissed off at me, then, dragged me out to the yard and tied me between two trees, gagged me with my clothes, and...well, the rest doesn't have anything to do with what you want to know.
I don't know if that's what you were looking for; feel free to send me a private or email message if you think I could provide any more help.