Genesis 4:10

What hast thou done? The same question as that put to Eve (Genesis 3:13). This question has been put by the voice of conscience to every murderer since Cain; it had a special force in reference to the first man done to death by his brother.

the voice of thy brother's blood Probably it would be more accurate to translate, as Driver, "Hark! thy brother's blood, &c." The word "blood" in the Hebrew is plural, and the word "crieth" is in the plural agreeing with it. The Hebrew for "voice" (ḳôl) should similarly be rendered "Hark!," instead of "noise," in Isaiah 13:4, and instead of "the voice of," in Isaiah 52:8; see Heb. Lexicon.

The Hebrew idea was that blood shed, for which there was no avenger, cried to Jehovah for vengeance against the murderer. Jehovah has learned of Abel's murder from the cry of his blood spilt upon the ground. Another Hebrew belief was that, if only the blood were covered with earth, it would be silent. Cf. Job 16:18, "Oh! earth, cover not thou my blood and let my cry have no resting-place"; Isaiah 26:21, "The earth also shall disclose her blood, and shall no more cover her slain"; Ezekiel 24:7. To this ancient supposition there is an allusion in Hebrews 12:14, "the blood of sprinkling that speaketh better than that of Abel."

"In the picturesque legend of the Arabs, there rose from the blood (or bones) of the slain man the -death-owl," which shrieked, -Give me to drink," until it was appeased by the blood of vengeance." (Gordon's Early Traditions of Genesis, p. 203.)