Doris is a nine and a half week old Miniature Schnauzer puppy that has shown no sign of aggression until last night. (Olive (her mum) shows only one aggression towards certain men, not sure who but she growls at a few men but never women.) Yesterday afternoon Samson her last brother left for his new forever home and she was fine for an hour. Doris then started growling when we picked her up from her being on the floor, in her pen and playing with her mum. She only developed this behaviour last night and she has now bitten a guest and also us. She growls and shows her teeth, but I see no physical signs of aggression (tail down, ears back or licking lips). I just walked into the bedroom where she is and she has chewed up the puppy pad torn up some vet bed and also tipped her water bowl up what should I do for punishing her for this behaviour? I was wondering could it be because of her brother leaving her/Separation Anxiety? Any comments welcome, as we want to get to the bottom of this behaviour ASAP and get her out of this awful habit before she does real damage.