Two vids of the same person doing a single arm and two arm heavy jerks, for comparison of body angle etc during the jerk. A deliberate choice of vids where heavy KBs are being used in order to show good technique with the heavy KBs.
Note the hand position/grip or lack thereof in the two hand jerk. Many books state that the wrist should remain straight, however, the rules are not being broken because the forearm bone is still taking the weight due to the position of the KB on the edge of the palm even though the wrist is "bent" backwards; important points to watch.
Two arm jerk:
One arm jerk: