Speak tartly: "Those are identical!" (4)
I believe the answer is:
snap
'speak' is the definition.
(I know that snap is a more specific form of the action speak)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for snap that I've seen before include "on the spur of the moment" , "sometimes preceded by brandy" , "A walk in the park < to shoot" , "type of election" , "Break suddenly with cracking sound" .)