I don't think I've not seen this mentioned yet, but it really appears as though the Mud in the middle of the picture is missing a few fingernails. Note the comparison between his nails and where I'm pretty sure they're missing (green and red respectively)
http://imgur.com/a/0IQx0
EDIT: A friend suggested this could be some sort of Fuzzle security system. It appears to be inside the barbed wire? I sort of see how it could be, but at the same time maybe not.
http://imgur.com/a/E1nNu