That's the smashing part of the heel on both these images, and it gets worn away. In fact, I've seen them wear away their heel all the way to the flesh.
在这些图片上，也确实可以看到跟部的破坏。 确实，它开始剥离。事实上，我已经看到了他们的抛离。 他们的跟部外壳脱离了肉体。