Elderling Creations Theory (Spoilers through all the books and Dragon Haven)

[maulkin]

As it was in the shape of a skull, I just imagined that it may have an ability to verbally communicate UNLESS, if the skull is merely painted on or there is no shaped 'mouth' then, it could be similar to the Tarman in that it is unable to 'talk', as such.

Many skulls are depicted simply as the cranium, without the lower jaw. If shaped in this way then the skull charm would still lack a mouth. A skull, even when in possession of its lower jaw, is unable to speak, lacking tongue, lips, lungs and brain. Perhaps a charm can only speak if it possesses features associated with speech. Skulls also lack eyes and ears, so perhaps the skull charms are deaf and dumb. Skulls are associated with death, which presumably allows the charms to kill the unborn offspring of their wearers. As to how they kill, the possibilities are quite disturbing. Perhaps they absorb the embryo's life force in a similar manner to the stone dragons or perhaps the proximity of wizardwood marks the embryo in a similar manner to the rainwilders, causing it to mutate to the point where it is no longer viable.