Split Wood At Branch Attachment Showing Decay

Love these photos and images of the inside of wood.  It always surprises me how symmetrical the two halves of split wood can be.  Its never deliberate to "get the wood" to split this way but it must say something about weak points in the wood for it to keep happening.  And my splitting maul.....

the wood in the pictures is upside down, the Flame shaped dark wood is the area of split wood at branch attachment showing decay