What a farmer might do to hearten the cassowary? (3)

I believe the answer is:

sow

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'what a farmer might do to hearten' is the definition.
The definition suggests a singular noun which matches the answer.

'cassowary?' is the wordplay.
'SOW' is hidden in amongst the letters.
But, I'm not sure how this is indicated.

'the' acts as a link.

Can you help me to learn more?

(Other definitions for sow that I've seen before include "Plant seed in soil" , "Plant seeds for the pig" , "swine" , "Female bear" , "One who takes care of litter" .)

I've seen this clue in the Evening Standard.

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