Cold-blooded specimens left us scratching heads (4)

I believe the answer is:

efts

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'cold-blooded specimens left us scratching heads' is the definition.
I can't judge whether this definition defines the answer.

'specimens left us scratching heads' is the wordplay.
'specimens left' becomes 'e' (I can't explain this - if you can you should give a lot more credence to this answer).
'us' becomes 'ft' (I've seen this in other clues).
'heads' indicates taking the first letters.
The first letter of 'scratching' is 's'.
'e'+'ft'+'s'='EFTS'

Can you help me to learn more?

(Other definitions for efts that I've seen before include "Kind of newts" , "Amphibians" , "Old lizards" , "Baby newts" .)

I've seen this clue in The Independent.

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