Patellar reflex (4,4)

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4,4

knee jerk

'patellar reflex' is the definition.
(synonyms)

This is all the clue.

(Other definitions for knee jerk that I've seen before include "instinctive" , "Such a predictable reaction" , "Sudden and ill-considered" , "Spontaneous" , "Type of automatic reaction" .)

I've seen this clue in The Times.

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