Observe bat in wonder? (3-6)

I believe the answer is:

eye opener

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'wonder?' is the definition.
(I've seen this before)

'observe bat' is the wordplay.
'observe' becomes 'eye' (I've seen this before).
'bat' becomes 'opener' (I can't explain this - if you can you should give a lot more credence to this answer).
'eye'+'opener'='EYE-OPENER'

'in' is the link.

Can you help me to learn more?

(Other definitions for eye opener that I've seen before include "takes the lid off?" , "unexpected revelation" , "Surprising revelation" , "wake-up call?" , "one lifts the lid?" .)

I've seen this clue in The Telegraph.

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