One variety of a human malformation or "monster": A zoomyle includes uterine moles which are abnormal developments of the placenta during pregnancy and also known as, "hydatidiform moles".

The "mole" may consist of multiple cysts which develop in the placenta so that it appears like a large bunch of grapes. One complication is an invasive mole, in which the abnormal placenta penetrates through the wall of the uterus and damages it to the point where a hysterectomy is necessary. More seriously, four percent of women develop cancer in the abnormal tissue (choriocarcinoma).

This is a term which was coined by Geoffrey Saint-Hilaire (c. 1857) for a variety of human-body malformations.