This condition — known as bicephaly — is an uncommon abnormality that occurs during embryonic development, when identical twins fail to fully separate, Live Science previously reported. The condition appears in all sorts of animals, including deer and porpoises; humans seem to encounter living bicephalic snakes about once a year. In 2019, a bicephalic baby rattlesnake named "Double-Dave" turned up in New Jersey, while a two-headed viper slithered onto a family's property in Virginia in 2018. Dos just helped 2020 meet its quota. Bicephalic animals tend to have a rough go of it in the wild, where their competing brains...