My sister and our dog

One day I came home from work early and I thought no one else was home. I heard noises coming from my sister’s bedroom so I went by her bedroom door and peeked in. I was shocked to see her and our family dog together on the floor. My sister was nude and she had her legs wide open and the dog was licking her between her legs. She was moaning and saying good boy you are such a good boy while rubbing his head which was between her legs. I decided to walk in and confront her. When I opened the door she looked up at me and tried to push the dog away leaving her sitting there in front of me totally nude with her legs wide open. I said how long have you been doing this? She yelled for me to get out. I laughed at her and said okay but Mom and Dad are going to love to hear about this. She said please don’t tell them please. I asked her why should I do anything for you. You never do anything for me and your always mean to me. She asked me what I want not to tell on her. I thought about it and said I want to watch you have sex with the dog. She said no way and I said okay I’m telling Mom and Dad. Okay okay but promise me you will never tell them. She was almost crying so I said okay but you have to promise to allow me to watch you. I closed the door and sat on the bed and said okay I’m ready. She looked so upset and ashamed of being caught and now completely naked in front of me. She opened her legs again and fingered herself calling the dog to her. He immediately went to her and smelled her vagina and started to lick her vagina again as my sister put her head back as soon as the dog was licking her. Her eyes were closed so I took out my phone and opened the camera and took pictures of her and the dog without her knowing what I was doing. I found myself getting sexually excited seeing her like this. I said now I want to see you have sex with him. She turned around got on her hands and knees and started to slap her bottom. The dog smelled better her legs licked her a few times and climbed up on to her back and she took her hand and grabbed his penis and put it into her vagina. I couldn’t believe how fast hard and deep the dog was having sex with her. My sister had her face on the floor and the dog was going so fast I thought he was going to push her across the room. Finally my sister moaned really loud as she had an orgasm and the dog f****d his knot into her vagina. The whole time I was taking pictures of her and the dog without her knowing.
This is my story about how I caught my sister and our dog having sex.