That's actually the safety. When you grab the grip it lays flat and arms the weapon. The moment you hand comes off it a spring throws it back into the on position and locks the trigger directly. You can find something similar (although a little more complicated) on the M1911 handgun and UZI, they just aren't as large because they operate slightly differently (by locking up the firing pin or bolt.) Because the weapon is a bullpup, the action is in the wrong place to use that system, so i just made it engage the trigger and worked in enough space so that even if your grip isn't perfect, as long as it's 2/3 of the way depressed, it will still disengage.