Avraham's Laughter

Abraham and sarah were already very old, and sarah was past the age of child bearing. So sarah laughed to herself as she thought, after i am worn out and my lord is old, will i now have this pleasure? Ait says, punch. We saw the same reaction from avraham in the last chapter when he was told he was going to have a son. But the rabbis teach there must have been something different about avraham's laughter and sarah's laughter. You're about to read more about that.