Lie next to reptile, we hear: one's got too close! (9)

I believe the answer is:

tailgater

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'lie' is the definition.
Both the answer and definition are singular nouns.
Maybe there's an association between them I don't understand?

I don't understand how the rest of the clue works.

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(Another definition for tailgater that I've seen is " One closely follows".)

I've seen this clue in The Times.

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