It is a "cud" most likely (bit of metal from previously minted coin pressed into this one) While a nice error coin, cuds do not usualy carry a premium though. It might even be a rather intersting die crack but same as for the cud, die cracks usualy don't carry any extra premium.
I could be wrong, but i have several 1960 and 1955 pennies i got from the error bin at the last local coin show and they are labeled as "cuds" as well as the "B i E" error penny I have also heard refered to as a cud rather then a die crack (though the bie is definately a die crack and not a cud) So it is entirely possible I am all wet about calling it a cud. Please if I am mistaken on this let me know.
A cud is a break along the rim of the die that extends into the field, and the OP's coin was not the result of "a bit of metal from a previous coin pressed into it". It is a die chip, pure and simple. To form the center of a letter or number, there has to be a "post" of metal on the die to keep it from filling with planchet metal. It is not unusual for this "post" to break off, allowing the planchet metal to fill the void. Chris
The original reply did say "cud", so i figured he was putting it in quotes because he knew it wasn't really a cud, but rather something most people call a cud anyway. Some people say 'internal cud', which i don't personally mind, but 'die chip' is the preferred terminology.
... Major Die Break or "Cud" always involves a breakage of the die that includes a portion of its shank and field and or design areas. In other words, it will involve a section of the die from its edge large enough to include some of the face of the die that has broken and fallen away or has been retained. If a die break occurs anywhere away from the edge (or neck of the die) within the field of coin design it is NOT a cud... hopes this helps...
No, it's not rare, but it does make a nice conversation piece or an example to show a young collector just starting out. Chris
If you can scribe the word "Yale" on that eight, you would have yourself a mighty fine looking padlock Chris. -Shaun