Final answer:
The foreign expression 'coup de grâce' means a finishing blow to something that has been getting weaker or worse.
Step-by-step explanation:
The foreign expression in bold, 'coup de grâce', refers to a finishing blow to something that has been getting worse or weaker.
In the context of the sentence, it describes how the dung beetle decapitates the millipede with its sharp plate-like structure on its face, ending the millipede's life. It is a final blow that concludes the beetle's feeding process.
It is important to note that 'coup de grâce' is a French term widely used in English literature to indicate a finishing or decisive action.
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