Honestly, when you are from this area when you say U.M. (or UM) no one thinks anywhere else. So I can see why they'd say U.M. and expect everyone to know. It is always my first assumption as well. I know there are obviously other UMs, but to us this is the only one that matters
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As to the pig, what a waste. I can't imagine why they'd roast a perfectly good pig and leave it around when people go to a lot of effort to get one for their caja china on holidays.