I think we discussed this when this “classic” SD column about twins originally appeared in 1996. http://www.straightdope.com/columns/read/2532/does-the-bible-tell-people-to-handle-snakes-plus (second question)
Other types of twins are:
superfetation (twins conceived at different times)
heteropaternal superfecundation (twins with different fathers)
half-identical twins: This occurs when the egg splits and the each half meets a sperm. They look very much alike but aren’t a 100% DNA match. Because the sperm is the difference, you can even have half-twins that are one boy and one girl. It is believed to be more common than once thought.
parasitic twins: conjoined but with one much smaller and less formed , sometimes just a limb, a head without a brain…(all kinds of weird cases of this).
semi-identical twins: a rare occurance in which one egg was fertilized with two sperm and then split. They are identical on their mom’s side but share only half their father’s genes. A pair was identified in 2007 in which one child is male and the other is a hermaphrodite (has both male and female genitalia) and is being raised as a female.
And then there are Ed Zotti and Cecil Adams
