Not reacting to interaction? (5)

I believe the answer is:

inert

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'not reacting' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for inert that I've seen before include "Motionless or inanimate" , "lazy" , "Lifeless, without power to move or act" , "Disinclined to act" , "Lifeless or static" .)

I've seen this clue in the Sydney Morning Herald.

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