I noticed that to and was thinking it was a bit odd. Good you pointed that out. Are those two heads closest to it always closed up like that? If so, this snail could be the cause and would warrent acction. Super glue would work, just dont get it on the heads of the Hammer.Just a thought, but it looks like it is growing under the skin of the hammer. I bet if you super glued the opening shut it would kill whatever it is!