Two sperms and two eggs can create fraternal twins. One egg, one sperm and some in-womb hocus pocus can create identical twins.
And what about two sperm and one egg? That creates trouble -- and a news story.
As the AP reports:
The unnamed babies, born in the U.S., may be the only infants of their kind ever seen. Apparently, live births of such babies have not been reported.
"It's extremely unlikely that we will ever see another case," said Charles Boklage, an expert on twinning at Eastern Carolina University in North Carolina.
But the babies aren't expected to survive.
