Cas heard her land though he didn't know what it was, at first. At first it sounded like a drunk coming home but Sam was the only one in the house who still drank and Cas couldn't remember him being drunk since he stayed with them.
Then it had to be... "Crowley." He got to his feet, pulled the blade for it's holster on his calf, and made for the nursery good when he heard his name. His name screamed. By Anna.
He didn't even think to correct her as she used his full name. He only dropped his blade nervelessly and ran.
She looked terrible, pale and manic. He couldn't tell if she was wounded but he was barely thinking as he clattered down the stairs. "Anna," he cried in relief as he took her in his arms. "You're safe, you're home. You're safe. You're home." He could barely breath in shock as he stroked her hair compulsively.