Hi, my 8 months old Whippet/ Cocker spaniel cross is usually very good with other dogs. He just loves to play chase and if a dog is bigger he is quite submissive with his body language. However, today we met a very young Collie puppy. My dog was suddenly really unfriendly and tried to nip the puppy and really had a go at him, growling! I have never seen him like this before. Does he just not like puppies? Or his he getting worse with other dogs generally because he is at that terrible "teenage stage"? Any advice or shared experiences would be great, thanks.