Snake that counts? (5)

I believe the answer is:

adder

'snake that counts?' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for adder that I've seen before include "1 of 21 [SNAKES]" , "Small poisonous snake, viper" , "He's making an extension" , "Venemous snake" , "calculator?" .)

I've seen this clue in The Sun.

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