Spot of trouble in its call (9)

I believe the answer is:

scintilla

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'spot' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'trouble in its call' is the wordplay.
'trouble' is an anagram indicator.
'in'+'its'+'call'='initscall'
'initscall' with letters rearranged gives 'SCINTILLA'.

'of' is the link.

Can you help me to learn more?

(Other definitions for scintilla that I've seen before include "little bit" , "Tiny hint, trace" , "suspicion" , "Tiny, scarcely detectable amount" , "scrap!" .)

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

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