This animal won't always die a natural death (7)

I believe the answer is:

opossum

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'this animal' is the definition.
(opossum is a kind of animal)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for opossum that I've seen before include "Large marsupial" , "Tree climber" , "American arboreal marsupial" , "Thick-furred marsupial of the Americas" , "Small Australian marsupial" .)

I've seen this clue in The Globe and Mail.

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