Mammal calculating tail not needed (5)

I believe the answer is:

shrew

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'mammal' is the definition.
(shrew is a kind of mammal)

I don't understand the remainder of the clue.

(Other definitions for shrew that I've seen before include "Woman to be tamed?" , "Small mammal with a long snout" , "Long-nosed mammal" , "Harridan" , "Mouse-like animal or scolding woman" .)

I've seen this clue in The Guardian.

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