Job 41:7

Canst thou fill his skin with barbed irons? - This refers to some kind of harpoon work, similar to that employed in taking whales, and which they might use for some other kinds of animals; for the skin of the crocodile could not be pierced. Herrera says that he saw a crocodile defend itself against thirty men; and that they fired six balls at it without being able to wound it. It can only be wounded under his belly.