The term "coup de grace," the blow of mercy, or killing blow, is correctly pronounced "ku de gras" where the final consonant sound in "grace" is clearly enunciated so that the word rhymes with "floss." The way that Bones pronounces it, "ku de grah", in her reconstruction of the attack on Leishenger, though a common mispronunciation, would literally mean "blow of fat," like Mardi Gras means Fat Tuesday. In French, a consonant is pronounced when followed by a vowel.
When Booth is at the port and has called for backup after realizing that Brodsky is there, he mispronounces his quickly deployed armed backup, the cavalry, as Calvary, the mountain upon which Christ was crucified. He does this several times throughout the series, including 2006's "The Superhero in the Alley" and 2009's "The Bond in the Boot"; it seems to be a habit of David Boreanaz.