I have a litter of 4 week old [puppies].  3 of them are affectionate and playful but 1 is very odd. She hasn't gained weight like the others  but she could take after mum and be more dainty in her genes. She is a bit of a loner and although she play bites  she shies away from the fights sometimes. She startles when you touch her sometimes and she walks backwards alot. The other pups all look up when I lean into the pen but she looks straight ahead. I've  questioned her eyesight, but her pupils seem to move  when you  look at her and I know eyesight  is still developing. I have tried a quick movement  to get them to blink but the other pups dont respond to this either  yet. Anyone had a pup like like this? Could she just be a late developer? She eats fine, moves to pee elsewhere,  and wags her  tail but she's  just different to the other 3 and my last litter.

Could she possibly be deaf.

I thought of that but when I hold her up and talk to her she moves her head and when you go to the pen and talk she stirs with the others and starts to move. Its difficult  I suppose  to tell  whats following  behaviour  but I'm  sure she can hear.

I thought perhaps she's deaf but whatever's going on, maybe it's time to have your vet take a look.   Walking backwards?   Yes, odd.

Sounds like it could be something neurological but I'm not sure what you can do other than wait and see.... and get a vet check.