I think I know what you mean but is there any way you can post a picture? I have seen this on some of the strays I have found. I think its the beginning of polydactyl toes but they aren't quite formed right. Polydactyl is a result from inbreeding I believe. I am sure it doesn't occur on all inbred cats some probably get extra claws or even deformed paws and some probably have normal paws and claws.