Phoebe, my 12 year old cocker has suddenly started to be aggresive with Izzy, for no apparent reason. She went for her in the car today, after they'd been happily running in the woods, and was a bit growly this evening, then she had her pinned down on the floor, really snarling. Izzy isn't hurt but clearly bewildered, and frightened. I have wondered if perhaps Izzy is coming into season as Phoebe has been sniffing her bottom and her wee. Do bitches react to other bitches in season, or should I be looking for another cause? I have had no issues before this, once Phoebe accepted Izzy after about a week of her coming home. I'm very concerned and will keep them apart when I'm working tomorrow.