Alien Swarm/Weapon one and Weapon two
Alien Swarm is rife with various tools, weapons, and miscellaneous items that can help you destroy the Swarm, heal your allies, or a myriad of other special effects.
Upon selecting a campaign to play, players are prompted to select both their character and a choice of two primary weapons, as well as a single secondary weapon. The two primary weapons can be changed at will; the secondary item is used by pressing the 1 key.
Aside from the left mouse button, which uses the default fire mode (for example, the standard assault rifle simply shoots bullets), it is possible to click in with the mouse wheel to execute the weapon's alternate firing mode, assuming it has one (for the above example, the assault rifle would fire a grenade which detonates on impact with a target or the ground). Right-clicking allows players to execute a melee combo attack which is effective against enemies too close for enemy fire. Much like other Steam games, friendly fire cannot be disabled, and on higher difficulties can be the bane of players. Using the melee prevents friendly fire.
When a reload order is issued, either through running out of ammunition in your given clip or manually (R by default), a small gauge appears at the centre of the screen. Hitting R when the cursor is over the white highlighted section of the bar will prompt the character to perform the reload far faster than usual. It is accompanied by a white flash on the weapon's muzzle and possibly a character quote. Failing to hit the reload button at the right time causes the weapon to jam and become unusable for a longer period of time. Avoiding the reload button entirely performs a standard reload. This fast reloading method is necessary to obtain the Quick Reload and Gunslinger achievements.
