Lp2 Doubled Die

Please, could someone explain why what looks like a die chip (like on the State Quarter "extra tree branch" "error") is being called a doubled die? I can't see any doubled elements on these coins except for - usually - one extra digit on the hand. Perhaps this is just an extra-sensitive area on the die, but a die chip certainly doesn't warrant a designation as a DD.

If someone who really knows (Chuck, Bill, Mike) really say these are actual doubled dies, then please explain how they warrant that ? Inquiring minds and all that..:P

lol.. that doesn't tell me why they are a doubled die, though

I found 7 of the WDDR-004 in 1 of my rolls. They weren't nearly as easy to see even with the loop as the WDDR-002 that I purchased. I have another roll with a WDDR-004 on the end, but I'm not going to break it open.