When Sanchez is having trouble breathing, Toby tells happy to feel down from his collar-bone on Sanchez's back. The collar-bone or Clavicle is on the front of the torso, the bone he is referring to (and the one that Happy finds) is the shoulder-bone or Scapula.
When the armed drone in the trailer shoots its way out, the door falls open. However, the cam style locking mechanism would not open after being shot, even if the locking bar was shot apart. It would only open if the bar was rotated.