John Gill Commentary Job 29:9

"The princes refrained from talking, And laid their hand on their mouth;" — Job 29:9 (ASV)

The princes refrained talking
Who were in court before Job came in, and were either talking with one another about indifferent matters, or were giving their opinion in a case before them; but no sooner did Job make his appearance, but they left off talking, and would not proceed any further; they laid a restraint upon their words, and curbed themselves from speaking any more till they had heard his opinion:

and laid [their] hand on their mouth ;
as a token of silence, (Judges 18:19) .