What they told me was the almost perfectly circular "ring" on the face of the skull was where the snare cut into the bone for a long lingering and miserable death.

Whether or not it's true I don't know, but I stare at that picture and I can (unfortunately) see it happening.

It was a small skull, so yes it was calf, which may mean the bone was more pliable/growing and subject to intrusion by a foreign object. The circular ring is too perfect to be made by any other means that I can think of.