The dog

Why didn't the mother do anything when she looked out the window and saw Carl being rough with the dog? And when the dog turned up dead, why didn't anyone question how he died and how he ended up that way? Dogs aren't perfectly healthy one minute and dead in a dumpster the next. Wouldn't most people wonder how their dog ended up like that? Wouldn't most people think about the last time they saw the dog alive? In this case, the last time she saw him alive was when she saw Carl being rough with him. It seems like they would have made the obvious connection at dinner when Carl was acting like the dog could easily be replaced and there was nothing to be sad about. The mother would know it was Carl who did it.