End of kitten's tail is only JUST attached?

Our female cat just gave birth to 6 beautiful kittens in the night, but one of them, the end of the tail looks like a string that has only been cut half way through and not all the way. There's no blood and it's not in any pain. It's eating and sleeping like it should, and there weren't any birth complications with it.

Could it have been the way it was sitting in the womb and the circulation was cut off to the end? Or is it something to worry about? It looks like the tail is complete (no bone exposure) but it's got a little add on hanging from the end.

Could be a birth defect, or mum accidentally chewed it. This is from the deliberate brother & sister mating isn't it?

I'd be at least phoning the vet and see what they think.

One little one from our newest group of "feral" kittens had the tip of his tail all scabbed over when we brought him in. A few days later that part fell off. No blood, no screaming, nothing. Just a shorter round-tipped tail that's bald for now but there's a little hair growing on it. Maybe momma kitty accidentally bit the tail while cleaning up/removing the umbilical cord