My first experience with any animal was when I was 16. I was spending the weekend with a couple of guys that were in their 20s. They had a large mixed breed dog that they had trained to fuck girls. I had spent a few nights with them before and met the dog but had no idea it was trained, and at 16, I had not really been exposed to bestiality in any way. 

  Saturday afternoon and they had me ass up on the floor. I expected one of them to drive into me again, instead the dog mounted me. I almost pulled away, but one of the guys put his hands on my shoulder and told me to stay still. The other guy guided the dog dick to my pussy. I was disgusted and a bit freaked out by it, but I had learned to give men what they wanted in order to please them, so I stayed still. 

  The dog was humping wildly at first and his dick was hardly out of its sheath, so it kept falling out of me. The guy kept guiding it back in. It was not long before the dog dick had grown enough that it no longer fell out. The rapid humping and the dog's side to side movements as he seemed to be shifting feet all the time, had his dick rubbing all sides of my vagina. 

  Being my first, I did not know anything about the knot. When that big bulge first hit against my labia, I had no idea what it was. I actually thought for a moment that one of the guys was trying to push his dick in too, or maybe it was his hand. It smacked against my pussy's lips a couple more times before it actually pushed between them. Combined with the stimulation of his dick rubbing my vaginal walls, the knot between my cunt's lips had me moaning. 

  The knot pushed in and slipped out a few times. I realized it was getting bigger, but I really did not understand what that meant. When it pushed into me and would not slip back out, I started to panic. That hand on my shoulder and the reassuring voice telling me it was okay and normal alleviated my fear and panic, though I still was not sure I liked it. As I calmed, I began to feel the knot throbbing, and it was situated right on my g-spot. It did not take long before the stimulation pushed the fear completely away. 

  I could feel the dick growing inside me. It stretched deeper and got fatter. Though the dog was not humping any more, the throbbing in the knot and dick as more blood was being pumped into it was getting me quite excited. An orgasm was building. My moans had resumed and were getting louder. The dick pressed against my cervix. It was as though the throbbing was suddenly vibrating all through me. My body trembled and I screamed as the orgasm raced through me. 

  Another orgasm ran through me a few minutes later, stronger than the first, it had me shaking and screaming out how good it felt. Then it happened. The dog dick exploded inside me. The force of the cum splashing against my cervix obviously caused it to push through. I felt the cum inside my womb. For a few moments I lost it. My body rippled and shook. I screamed and shrieked. More and more cum filled me and I continued to climax for what seemed like hours. 

  I am not sure how long the dog stayed locked to me, but eventually the knot did slip out, and when it did, I collapsed. I was very content, happy and filled. By the time the dog finished filling me with cum, and his knot slipped out, I knew I would have to do that again.