Crawler unsettles, endlessly uncovered (11)

I believe the answer is:

rattlesnake

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'crawler' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'unsettles endlessly uncovered' is the wordplay.
'unsettles' becomes 'rattles' (I can't explain this - if you can you should believe this answer much more).
'endlessly' means to remove the last letter.
'uncovered' becomes 'naked' (I've seen this before).
'naked' with its last letter removed is 'nake'.
'rattles'+'nake'='RATTLESNAKE'

Can you help me to learn more?

(Other definitions for rattlesnake that I've seen before include "Sidewinder" , "Venomous creature" , "Potentially lethal reptile" , "Poisonous (and noisy!) reptile" , "Poisonous creature" .)

I've seen this clue in The Daily Express.

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