Speak in vain now the beasts are excited (5,4,6)

I believe the answer is:

waste ones breath

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'speak in vain' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'now the beasts are excited' is the wordplay.
'excited' indicates anagramming the letters.
'now'+'the'+'beasts'+'are'='nowthebeastsare'
'nowthebeastsare' with letters rearranged gives 'WASTE ONES BREATH'.

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(Other definitions for waste ones breath that I've seen before include "Give advice in vain" , "It's useless" , "so to speak" .)

I've seen this clue in The Daily Express.

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