My littermate girl cats age almost 3 years old (Millie and Tillie) have started to be aggressive suddenly. A few months ago Tillie got scared/jumped off the couch and hissed ...Millie responded with hissing and they ended up in a heated cat fight that lasted a few seconds. It happened again a week after that and my poor dog was in the middle of it, the cats turned on him after hissing at one another and we had to break it up. For 4 months nothing like this has happened... until tonight. I picked Millie up to hold her and she let out this weird meow that I have not heard before. Tillie came running when she heard Millie's strange meow. I kept holding Millie and she did the weird meow again. As I went to put Millie down, Tillie hissed at me and because of that Millie started hissing. I started to walk away from them to give them space and they started to do the hissing fighting thing with each other but a few seconds later Millie lunged and attacked my leg and left some nasty bloody slashes on me. I do not know what to do, or know what has caused them to start doing this. It seems like the cats feed off each other but have never lunged and attacked me before. Any insight would be helpful!