Says nothing just does what a good dad does (5,3)

I believe the answer is:

keeps mum

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'says' is the definition.
The definition and answer can be both to do with communicating as well as being verbs in their -s form.
Perhaps they are linked in a way I don't understand?

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for keeps mum that I've seen before include "If one behaves filially thus" , "stays silent" .)

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

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