I've heard of sister friend,but not this.

Anyone who is around Sammy knows that the biggest part of him is his heart. Anytime I don't feel well he frequently checks on me and often wants to lay by me until I am feeling better. It was no surprise when CupCake wasn't acting herself that he wanted to provide her with comfort. So there the two of them were laying in bed snuggled up together and I hear Sammy starting to sing her a song. I don't remember every word but it went something like this " CupCake I love you and you're my sister dog. You're my sister and my dog." He is just so precious and sweet.