Be snagged on twig (5,2)

I believe the answer is:

catch on

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'twig' is the definition.
(synonyms)

'be snagged on' is the wordplay.
'be snagged' becomes 'catch' (I can't justify this - if you can you should give a lot more credence to this answer).
'catch'+'on'='CATCH ON'

Can you help me to learn more?

(Other definitions for catch on that I've seen before include "twig" , "Understand - become fashionable" , "Get it" , "Informally, become popular or come to understand" .)

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

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