What important revision did Shakespeare make to his will as noted in the biography, Will in the World?

Shakespeare's will, written a few months before he died and revised a few weeks later, is significant for what it doesn't include as much as for what it does. Specifically, in the original will his wife Anne is left absolutely nothing - all Shakespeare's wealth and property is left to his daughter, Susanna. In the revision, however, Shakespeare leaves Anne his "second best bed", one of the most famous legacies of all time. The exact reasons for this very specific legacy have never been absolutely defined, but the author of Will in the World makes several plausible suggestions. It certainly has the air of an insult, but one never knows - particularly where Shakespeare is concerned.