Jamieson, Fausset and Brown on Job 31:40

40. thistles--or brambles, thorns.

cockle--literally, "noxious weeds."

The words ... ended--that is, in the controversy with the friends. He spoke in the book afterwards, but not to them. At Job 31:37 would be the regular conclusion in strict art. But Job 31:38-40 are naturally added by one whose mind in agitation recurs to its sense of innocence, even after it has come to the usual stopping point; this takes away the appearance of rhetorical artifice. Hence the transposition by Eichorn of Job 31:38-40 to follow Job 31:25 is quite unwarranted.