Rule 5

Never try to catch a dropped gun.

When you do, things like this happen.

...he bumped into Sollman as he was leaving a closet-sized room with a total of three men inside. Renninger fumbled the gun after bumping Sollman, grabbed to regain control of the 40-caliber pistol, and, in doing so, the gun went off, sending a bullet into Sollman’s back.

H/T to Sebastian.