Albert Barnes Commentary Job 41:23

"The flakes of his flesh are joined together: They are firm upon him; they cannot be moved." — Job 41:23 (ASV)

The flakes of his flesh are joined together - Margin, “fallings.” The Hebrew word used here means anything “falling” or “pendulous,” and the reference is probably to the pendulous parts of the animal’s flesh: the flabby parts, the dewlaps. In animals, these parts around the neck and belly are commonly soft, pendulous, and contribute little to their strength.

The meaning here is that in the leviathan, instead of being thus flabby and pendulous, these parts were compact and firm. This is strikingly true of the crocodile. Its belly is, indeed, softer and more penetrable than the other parts of its body, but there is nothing like the soft and pendulous dewlaps found in most animals.