Question

what is the meaning of the foreign expression in bold?
deltochilum valgum, a species of dung beetle, prefers to eat millipedes rather than dung. the beetle uses its long back legs to grab the millipedes body before delivering the coup de grâce: it decapitates the millipede with its clypeus, a sharp plate on its face that acts like a chisel.
a finishing blow to something that has been getting worse or weaker
a destructive or catastrophic chain of events
a deciding factor that significantly changes an events outcome
an action that overwhelms something that has been flourishing

Explanation:

The phrase "coup de grâce" is a French expression. In the context of the sentence, the dung beetle uses its clypeus (a sharp plate on its face) to decapitate the millipede. This action is the final blow that ends the millipede's life. The first option "a finishing blow to something that has been getting worse or weaker" aligns with this context as the beetle is delivering the final, fatal blow to the millipede (which is likely weakened after being grabbed by the beetle's legs). The other options do not fit the context as well. The second option about a "destructive or catastrophic chain of events" is too broad and not specific to a single final blow. The third option about a "deciding factor that significantly changes an event's outcome" is more about influencing an outcome rather than being a final, fatal action. The fourth option about "an action that overwhelms something that has been flourishing" is incorrect as the millipede is not described as flourishing but rather as being attacked and then receiving a final blow.

Answer:

a finishing blow to something that has been getting worse or weaker