When taking a weapons box (or salvage box) during an online match, all players in the match get the weapon (press TRIANGLE or Y at the end to see salvaged weapons) regardless of who picks up the box. However, the notification of what you get doesn't appear on your screen.
Unlock one of the following Pesticide guns as a reward for reaching Rank 8 with any of the four corresponding Armor classes. Note: Reaching Rank 8 is only possible under the Inferno difficulty setting:
When low on health and there are no health pick-ups, use friendly-fire to kill the player. Then, revive him. Reviving a player restores him to their full health, and may be something to consider on the Inferno difficulty.