The ice cube formed this strange limb through a process that can be described as differential freezing. The outside, and bottom of the ice cube froze quicker than the center. And as you know, water expands as it freezes. Evidently, there was a small hole in the top of the cube as it the cube froze, and as the center of the cube froze, it caused a small icicle to be pushed up from the cube.

Cool, huh?