The Developer Commentary is an extra mode in Left 4 Dead. In it, a player is able to listen to audio comments made by the developers, while they play through a campaign in the game with a significant lack of difficulty, as all Infected will ignore the player and only attack the AI Bot Survivors. The mode takes place in No Mercy with icons called Commentary Nodes throughout a campaign, which trigger a specific audio comment when the player presses the "use" key while looking at the icon. Some Commentary Nodes, when activated, will spawn objects, characters, and even scripted events. Though there are enemies in the game, there are no Special Infected unless the player has spawned them by a node, and the Common Infected generally ignore the player as mentioned until the finale. If all of the AI Bots are dead, spawned Special Infected will target the player. Due to this, no Achievements may be earned, but it is a way of practicing a number of skills.