These animals are insensitive to pats when powerless (7)

I believe the answer is:

numbats

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

'insensitive to pats when powerless' is the definition.
I can't tell whether this definition defines the answer.

'these animals' is the wordplay.
'these' becomes 'num' (I can't justify this - if you can you should believe this answer much more).
'animals' becomes 'bats' (bat is a kind of animal).
'num'+'bats'='NUMBATS'

'are' acts as a link.

Can you help me to learn more?

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

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