They show surprise that there's twice as many pockets (6,5)

I believe the answer is:

double takes

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'they show surprise' is the definition.
The definition suggests an adverb but the answer is not.

'there's twice as many pockets' is the wordplay.
'there's' is a charade indicator (letters next to each other).
'twice as' becomes 'double' (synonyms).
'many pockets' becomes 'takes' (I am not sure about this - if you are sure you should believe this answer much more).
'double' put next to 'takes' is 'DOUBLE TAKES'.

'that' is the link.

Can you help me to learn more?

I've seen this clue in The Irish Times.

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