Henry is correct. Grease filled die. Unfortunately, you'll find many die issues from the 40's and 50's wheat ears. I have a few hundred of these types of coin with different die type issues. The only one that I've found is slightly collectable is the BIE version you normally find in the 50's wheats. I'm not saying you've won the lottery if you find one, but they are worth just slightly more than a normal wheat.