Attendance by a brain shows composure (8,2,4)

I believe the answer is:

presence of mind

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'composure' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Perhaps you can see a link between them that I can't see?

'attendance by a brain' is the wordplay.
'attendance' becomes 'presence' (presence is a kind of attendance).
'by' becomes 'of'.
'a brain' becomes 'mind' (synonyms).
'presence'+'of'+'mind'='PRESENCE OF MIND'

'shows' acts as a link.

Can you help me to learn more?

(Other definitions for presence of mind that I've seen before include "alertness in crisis" , "Wits are required to display such" .)

I've seen this clue in The Daily Express.

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