A bit of a racket in pearls or horses (6)

I believe the answer is:

string

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'horses' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for string that I've seen before include "Length of narrow cord" , "Sequence; cord" , "light cord" , "might one be plucked?" , "Number of animals" .)

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

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