The rat lied about pointless warning (4,6)

I believe the answer is:

idle threat

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'pointless warning' is the definition.
'idle threat' can be an answer for 'warning' (thesaurus). I'm not sure about the 'pointless' bit.

'the rat lied about' is the wordplay.
'about' indicates an anagram.
'the'+'rat'+'lied'='theratlied'
'theratlied' anagrammed gives 'IDLE THREAT'.

Can you help me to learn more?

(Another definition for idle threat that I've seen is " Unconvincing menace".)

I've seen this clue in The Daily Express.

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