Haha! That's funny. :p Something very similar happened to me when I was younger (maybe around age 16?), with my cousin Michael. He was staying with us for a couple weeks during the summer, and we had mattresses pulled out into the living room so that my younger sister, he and I could all stay in the same room together.
One morning, I woke up to him talking to my mom in her room, and he sounded worried. He was saying, "I think she's possessed. She was growling in her sleep and wouldn't wake up," or something very much along those lines (can't remember verbatim). I thought it was hilarious, and started laughing to get their attention. Even as fanatically religious as my mother is, she didn't think I was possessed, and we eventually just comforted him with saying that I make weird noises in my sleep.
I do talk and argue in my sleep, as well, so I think that I'm just very vocal during sleep---whether that be "animal" vocalities or "people" vocalities. LoL