Well, poot, as my mother used to say:

This is the water endstone.  I made the mistake, the day of the pouring, of picking it up to remove the cardboard form.  It crumbled.  The others seem to be fine, so I’m left to wonder whether I added too much water to the bucket for this one or I just should have waited to disturb it.

Not a problem: I have 30 pounds of concrete mix left.  I can make another one.