A dog who tenses up and falls over when he's excited or scared has left vets puzzled about the exact cause.

Peter the cocker spaniel has been turning heads around Sheffield due to the behaviour, with triggers including birds, ducks, bikes, other dogs and crunchy leaves.

Emma Clayton, the dog's owner, said vets have told her Peter didn't seem to be in any pain but more tests were required to pinpoint the reason behind it.

She said: "He's perfect in every single way, even with this silly little quirk he's got."