Their noise increased to a chorus of baas, upon which Oak pulled the milk-can from before the fire, and taking a small tea-pot from the pocket of his smock-frock, filled it with milk, and taught those of the helpless creatures which were not to be restored to their dams how to drink from the spout—a trick they acquired with astonishing aptitude.
There are no more uses of "aptitude" in the book.
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Hyde’s study indicates that girls and boys have the same aptitude for math.
Evidently she had great natural aptitude for her work.