Last night we had the smallest calf I have ever seen alive. He weighed less than twenty pounds, barely reached my knee. We were amazed that he managed to stand up and suck down a pint of milk. And sad, if not surprised, when he didn't make it through the first day. To cheer myself up, I took pictures of our twins. Well, tried to take pictures. Between them tearing around and their mother snorting and pawing dirt, I had a little trouble getting both of them in one frame.
As you can see, they're not identical. The one with the black spots on his face is a bull. That's called brockle-faced, and indicates a mixture of Angus blood and a white-faced breed like Herefords, which is called bald-faced, or baldy, which is not considered an insult to a cow, but I wouldn't recommend tossing it around in a biker bar.
The other is a heifer. She isn't quite a baldy because she has one black eye. When there is one twin of each sex, the heifer will usually be sterile. As a person who took over forty credits of college biology I should be able to give you a very detailed explanation of this phenomenon, but I'm drawing a blank and too lazy to go look it up. Plus, I'm sure one of my incredibly intelligent readers will explain it for you down in the comments.
There. I don't know about you, but I feel better about life in general.