Macbeth appears on stage and compares himself to a bear in a bear-baiting contest (i.e. he's in a serious jam).
History Snack: Bear-baiting is a blood sport that involves chaining a bear to a stake and setting a pack of dogs on it. Elizabethans thought this was great fun – bear-baiting arenas were located in the same neighborhoods as the theaters (just in case anyone wanted to take in a play and then top off their day of fun with a little animal cruelty).
Then Young Siward enters – when he sees Macbeth, he demands to know his name.
Macbeth's response? I'm "Macbeth" and you better be scared right now.
They fight and Young Siward is slain.
Macbeth talks some evil smack over the dead body, which goes something like this: Your swords and weapons can't touch me because you're "of woman born."