I upset her vampire bats - ignoring adult one who's expected to turn into a count, say (4,11)

I believe the answer is:

heir presumptive

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'count say' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?

I don't understand how the remainder of the clue works.

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I've seen this clue in The Independent.

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