The ominous sound of a 12-gauge shotgun
Panorama reporter Raphael Rowe visited Al's Army Navy store in Sanford, Florida - the town where Trayvon Martin was fatally shot in February - to find out about the type of weapon customers prefer for self-defence.
General Manager Fred Meltzer explained the appeal of a 12-gauge shotgun, loaded but not quite ready to fire.
Panorama: Kill at Will? America on Trial is on BBC One, Monday, 15 October at 20:30 BST and then available in the UK only on theBBC iPlayer.