I have a neat little story to share...
We had this Hereford cow, #2786, who calved her first calf in January 2007. Had it all on her own, in the snow. A little black baldy heifer. Next spring, 2008, we were checking the pregnant cows for calving and #2786 didn't look 3rd stage. Then later in May we saw that the bull was with her, and so decided to sell her the next time we took a load to the sale barn. But later that day, we saw that the bull had actually dislocated her hip (which is very very rare). She was barely ambulatory, so we knew she'd go really cheap at the sale barn for dog food. We decided that we'd take her to our processor for ground beef for ourselves, since she was still a young cow. Called up the processor, and he was booked out until September 15th. So we went ahead and booked that date. We put her in a little pasture by herself so that she wouldn't get bullied by the other cows, and brought her buckets of water and grain. Also bought a bagger lawn mower so we could give her the clippings from our yard. So we just kept on bringing her food and water twice a day. She was in a pasture right next to where we milked, so it worked out good. We'd just feed and water her right before or after milking every day. We were concerned that she'd lose weight, but she kept the weight on real well, even seemed to get bigger as time went on. As you can imagine, by the end of four months we were getting kinda attached to her. On the morning of September 14th, the day before the butcher date, we went down to milking. And there in her pasture, was a little black baldy bull calf, just standing there looking at us. We were absolutely shocked. We went in the pasture to take a closer look, and there was another black baldy calf, laying dead on the ground. The cow had TWINS! So we fed and watered #2786 (who was a lot thinner than she was the day before), milked the cows, and then hurried up to the house to cancel the date with the processor.
But can you believe that?! The DAY BEFORE her butcher date, she has TWINS!!! We had just seen her with the bull in May, so we weren't even checking her for calving. Her udder didn't get very big or tight, and her belly didn't get huge either. A cow pregnant with twins also calves about 10-14 days earlier than a cow with a single, so if she had been pregnant with a single we would have just taken her to the processor, only to find out she had a nearly full term calf! Not to mention she just barely made it under the wire... What if she had waited another couple days to have those twins?!