After reading a few of these recounts and stories, I decided to share my own.
I first DM'd this to FlaredCocknBust a few days ago and I thought, WTF, everyone on this forum ought to know about it. So, I've put it here for any and all to read.
Even though it was about 50 years ago, I can still vividly remember the day and the exact event that revealed to me my Zoophile desires. It was a summer day and I was lying own our front lawn with nothing but my swimsuit on. The neighbor's dog, who was a short legged, beagle-sized boy, came up to me and I petted him to say Hi. He was enjoying me scratching his back and rump. Then he got the idea to try to mount me on my legs. Because I was laying on my side, I could look down at him and see his nice pink penis extending from it's sheath as he was humping me. I had just recently learned to masturbate myself and wondered if it would feel good if I did it to him. I did nothing at the time since I was lying on the front lawn, but later that evening I asked my parents if I could sleep outside in the backyard. This was not unusual at all since it was a hot summer day and we had no air conditioning. I set up a sleeping bag on one of the canvas cots I used for this and went out to go to sleep somewhat earlier than normal. I stripped of all my clothes and climbed into the bag. I fell asleep but woke up around midnight. I figured this would be a good time to invite the neighbor's dog over for some fun. We had a solid redwood fence completely surrounding our backyard so the setting was pretty private. There was a gate in the fence connecting our two backyards, so all I had to do was quietly open the gate and whisper for the dog to come over. When he got into our backyard I could tell he was ready for some fun as he started humping my leg again. Since I was completely naked, I just sat down in the grass close as I could get to him. As he was humping my outstretched leg, I grabbed his cock and started really jacking him off. Boy did he go for it. I got him all the way out, with the knot, and laid back, face up in the grass and pulled him with his fully extruded, rigid dick over me and began to rub his cock as he was still coming on my erect cock. What a fantastic sensation that was, to have his hot, throbbing cock with all the doggy cum squirting on my dick and belly. I moved his cock up and down over mine and came in no time at all. - (I just realized I was filling my gym shorts with pre cum as I was typing this, so I just took them off - the memory is that vivid!! -)
I let him lick-up my cum and clean both of us as best he could - which was pretty thorough. I let the dog back into his own yard, he went slowly and begrudgingly, wanting to do it some more, then I crawled into my sleeping bag and slept well for the rest of the night.
As I typed this in I also started to realize that this is also part of why I prefer Cock 2 Cock frot (rubbing) as my favorite method of sex with both animals and men. With dogs I love rubbing mine on a nice, fully extruded, slick dog cock after I have masturbated him and he is still coming. I really love watching a dog with his dick fully out just continuing to cum and cum and cum, sometimes for over 15 minutes!