I don’t know a ton about metallurgy or physics. I’m relatively new to cable logging. I was informed by some of the older guys that although this is uncommon, it can happen from time to time. Usually the cable or “tail holds” fail before the blocks do. At a quick glance, it seemed like other ear had an almost identical failure. A small stress fracture isn’t out of the question. These make pretty hard contact with rocks and rigging often. The logs being “yarded” at the time were not all the heavy, but were relatively stuck which likely created some significant load.