Charles Ellicott Commentary Psalms 17:10

"They are inclosed in their own fat: With their mouth they speak proudly." — Psalms 17:10 (ASV)

They are inclosed ... —Literally, Their fat have they shut up. So Septuagint and Vulgate, without indicating the meaning. But the “proudly” of the next clause suggests that “fat” is only a figure for the conceit of prosperity, and as that verb is active, the word mouth should be joined with it as object from the next clause, “In their conceit they shut their mouth; (when they do speak) they speak proudly.”