Polonius tells Reynaldo to spy on Laertes and bait his friends by dissing Laertes' character. We never find out what happened to Reynaldo and it is never discussed again, probably because of Polonius' untimely death.
Later on, Polonius tries to bait Hamlet by sending his daughter, Ophelia, out into the open to see if Hamlet truly loves her. Hamlet answers that bate with the reply that he has never loved her and that she is a whore. However, other scenes and actions done by Hamlet seem to show that he does, actually love her.
The biggest bait of them all is probably when Hamlet tries to catch a guilty reply by Claudius during the play he made up. Hamlet reenacts the murder scene and it does strike Claudius' conscience. Claudius wails for light and quickly shuffles away.
Laertes later baits Hamlet by challenging him to a fencing match. This ends in everyone dying and ends the book.