By his head, in an oak. "Absalom was riding on his mule, and the mule went under the thick branches of a great oak. His head caught fast in the oak, and he was left hanging between heaven and earth, while the mule that was under him went on" (2 Samuel 18:9). Joab finds him there and thrusts three spears into him, against David's order to "deal gently" with the young man (18:5, 18:14).
A mule was the mount of royalty, so losing it from under him reads as losing the kingdom. Being caught by the head recalls the hair the text had praised four chapters earlier, so heavy he cut it once a year and weighed it (2 Samuel 14:26). Ten of Joab's men then strike him together, so no one man carries the killing (18:15).
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