It is vitally important to consider at what specific point the Chorus utters this speech that is so full of foreboding and ominous horror. Agamemnon has just returned, and Clytemnestra has gone off to meet him, praying to Zeus that her prayers would be fulfilled. This is an excellent example of dramatic irony, as the audience knows that she is planning to kill her husband in revenge for his sacrifice of their daughter, Iphigenia, to bring him victory in the Trojan War. However, the Chorus does not know what Clytemnestra is planning, and as a result, can only wonder at the feeling of incipient and inchoate terror and fear they sense. The reference to blood therefore effectively foreshadows the murder of their king:
But a man's blood, once it has first fallen by murder to earth in a dark tide—who by magic spell shall call it back?
Even though Zeus has apparently blessed Agamemnon and his forces with a victory against Troy, the Chorus pauses to reflect that when someone dies it is a permanent state of affairs and cannot be reversed. Even though Agamemnon returns in glory, the Chorus obviously suspects that his murder is approaching, and that when he is dead, nothing will be able to return him to life. The reference to blood therefore functions as something to increase the tension in the play as the audience waits to hear about what they know will happen.