This is one of the great encounters that Abraham has with God and a couple of angles.  They have dinner with Abraham and talk about Sarah having a child at this time next year.  Sarah, laughed, realizing how old she and Abraham were.  We will learn that nothing is impossible with God.  When Sarah was confronted about laughing, she denied it, but the LORD told her, "yes you did."  This was an awkward moment.  It's not good to laugh at God.