The Bridegroom of Blood
And it came to pass by the way in the inn, that the LORD met him, and sought to kill him. Then Zipporah took a sharp stone, and cut off the foreskin of her son, and cast it at his feet, and said, Surely a bloody husband art thou to me. So he let him go: then she said, A bloody husband thou art, because of the circumcision.

A lot of theories have been offered this passage, and a lot of questions, but rather than list them all I'm going to present what appears to be the most likely interpretation. Some of the questions (and their answers) are:

That's what the books say...but let us always remember: Any time something in any ancient document seems odd to us, the deficiency is more likely in our understanding than it is that the writer is out of their heads.