Query: On what body part was Kerry wounded on Mar 13, 1969?
Context: On March 13, 1969, on the Bái Háp River, Kerry was in charge of one of five Swift boats that were returning to their base after performing an Operation Sealords mission to transport South Vietnamese troops from the garrison at Cái Nước and MIKE Force advisors for a raid on a Vietcong camp located on the Rach Dong Cung canal. Earlier in the day, Kerry received a slight shrapnel wound in the buttocks from blowing up a rice bunker. Debarking some but not all of the passengers at a small village, the boats approached a fishing weir; one group of boats went around to the left of the weir, hugging the shore, and a group with Kerry's PCF-94 boat went around to the right, along the shoreline.