Crossword Genius

Sound petrified? (4,1,4)

Ross

I believe the answer is:

like a rock

I'm a little stuck... Click here to teach me more about this clue!

'petrified?' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'sound' is the wordplay.
I cannot quite see how this works, but
'sound' could be 'ear' (I've seen this in other clues) and 'ear' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

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