Looking surprised — as a snail? (4,3,2,6)

I believe the answer is:

eyes out on stalks

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

'as a snail?' is the wordplay.
I cannot really see how this works, but
'as' could be 'so' (I've seen this in other clues) and 'so' is found in the answer.
'a' is within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Guardian.

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