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The relationships in U.S. Acres are a little odd. Orson, the pig, is called "Mom" by the chicks Booker and Sheldon, I guess because he takes care of them for some reason. Roy, the rooster, is never said to be the father, even though he appears to be the only rooster on the farm. Then again, there are no hens on the farm that we ever meet, so I'm not sure who the mother is.
I also don't understand why Sheldon didn't get a stocking next to Booker's. Orson just put his own up there and forgot about it, I guess. Look, just because most of him is still in an egg doesn't mean he doesn't know when he's being left out.