Mary, Queen of Scots, shown with one head but not the other.

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Pronouns are useful tools, but may sometimes cause ambiguity in a hastily constructed sentence. An example (from a Wikipedia article):

Mary, Queen of Scots, at one time owned her head, which was subsequently preserved by Jesuits in the Scottish College, Douai, France, from where it was subsequently lost during the French Revolution.

Here is how to remove the ambiguity:

Mary, Queen of Scots, at one time owned St. Margaret of Scotland’s head, which was subsequently preserved by Jesuits in the Scottish College, Douai, France, from where it was subsequently lost during the French Revolution.