The name of this beast is variously given as anphivena, amphisbaena, amfivena, and many other variations. But the true spelling of its name is not the least of its mysteries; the exact nature of the amphivena’s form was also a source of considerable uncertainty.
The bestiary text tells us that this animal is so called because it has two heads, one in the ‘normal position’ and one at the end of its tail, and that its body forms a round shape. Isidore of Seville says that the amphivena can ‘move in the direction of either head with a circular motion’, which seems, understandably, to have been confusing to some bestiary artists. Pliny characterises it as a violent, poisonous beast, which might account for many of the depictions of it in the act of doubly attacking itself.