The Screams of Brahmin (quest)

The Screams of Brahmin is an unmarked quest in Fallout: New Vegas.

Detailed walkthrough
During conversations with certain Novac townsfolk, such as Jeannie May Crawford and No-bark Noonan, the Courier can learn of mysterious attacks at the nearby brahmin ranch. These conversations merely give more information, but are not required for the quest. In fact, the only way to initiate the quest is to speak to the ranch owner, Dusty McBride.

The ranch is located in Novac, to the south of Novac house or west of the Dino Dee-lite Motel. You can also find it to the west, on the left of the road which leads into the hills behind the town. Dusty McBride can be found inside the adjacent McBride house. He explains the situation, and advises the Courier to wait near the brahmin pen at midnight for the attacker, which is also mentioned in the note Midnight Ranch Attacks that he provides.

The attacker will appear as soon as the Courier exits the house. The assailant is a nightkin, who waits near the large boulder behind the house, hidden with a Stealth Boy. Targeting the area with V.A.T.S. will reveal his location. He will ignore the Courier, and at midnight will move to the pen and begin killing brahmin. There is no need to wait for this event; he can be attacked at any time.

The nightkin will remain hidden most of the time. He will only reveal himself while he is about to shoot at the Brahmin. The nightkin must be killed in order to advance. He is non-hostile to the player until attacked, but attacking and killing him has no effect on Karma. A holotape entitled The Screams of Brahmin can be found in his inventory, which goes some way to explain the attacks. After killing the nightkin, return to Dusty and speak to him again to complete the quest.

Upon completion, Dusty will give the Courier 75 caps and access to his freezer, which contains 9 or 10 brahmin steaks. Additionally, the Courier will gain Novac fame sufficient for Accepted status without any prior contact, and positive karma.

Behind the scenes
The title of this quest as well as the recovered holotape are a reference to the book and film The Silence of the Lambs, which features a protagonist who often cannot sleep because she hears the sounds of lambs screaming while being slaughtered.

Bugs

 * Even after you kill this nightkin and complete the quest, he can come back to life at a later date and stand cloaked and motionless near the train track. Targeting him in V.A.T.S will remove the cloak but he will not react or attack. Novac non-player characters will completely ignore him, even if you push him into the center of town.
 * On a similar note, the nightkin in question may revive at a later date where you killed him. It shall be uncloaked and non-hostile with all of his original inventory intact. This is useful for grabbing a minigun for sale or repair. It seems unable to equip any of its items and is thus an easy battle.
 * Sometimes the nightkin will respawn (or be replaced by another) and then proceed into Novac until it is waiting at the corner of the motel. It is not hostile but remains cloaked. If you speak to it, it may reply "One head gone, many heads to follow!" but do nothing else.
 * Sometimes the nightkin will go from his rock to the ranch as usual but will not attack the brahmin and only stand there cloaked (as if he forgot how to equip his minigun, and the script forbids him going closer to brahmin so he could melee the bovine). This happens when the nightkin was attacked by a nearby glowing one. In this case, killing him before he touches a brahmin will not solve the mini-quest. You have two possible solutions here: 1) If you've got the savegame before the nightkin was attacked by glowing one, fully close your game (simple reload will not help, the nightkin will still be bugged), then load, go kill the troublesome glowing one (sometimes it is somehow invisible but your companions are still able to attack it), proceed with your quest as usual; 2) Kill the bugged nightkin and proceed with your game, coming back to Novac from time to time - after a while the nightkin will respawn at his usual place and then you can try the quest again. *Addendum: It seems two conditions have to be met to keep this bug from occurring: 1) You must be within the fenced area, & 2) you must be crouched with the attempt at sneaking (even if you're detected). When he goes to fire, stand up and attack. This will keep the bug from occurring & complete the quest.
 * Another alternative is to try standing near the nightkin while it's cloaked during the day (behind a nearby rock) and use the wait function to fast forward until around midnight. After a few moments, it will hopefully pull out its minigun while still invisible, and proceed to attack the brahmin.
 * Talking to No-Bark about this quest or talking to the people about the Boone quest may cause the quest to become uncompletable.
 * If you kill the nightkin before he uncloaks himself and kills a brahmin, the quest may not be completable even if you retrieve and read the note. When returning to Dusty, there will be no dialogue option that states the threat is gone. Leaving long enough for the nightkin to respawn should give you another chance. The nightkin will approach at the appointed time from wherever he respawned. Only attack after he has fired on the brahmins, collect the note from his corpse again, and you should be able to complete the quest.
 * The nightkin doesn't attack the brahmin and just stands the other side of the fence, watching. When you approach the nightkin, he does nothing. You may stand as close as you want and no reaction will come from him. If you shoot him while he's still cloaked, you will be able to kill him (his dead body falls still cloaked), search him and gain XP from it but when you go back to Dusty McBride you only have the option to tell him that you haven't found anything.
 * [Only PC tested] Possible fix: Close the game and reload one of the closest saves where the nightkin haven't reached the pen yet.
 * Possible Bug "Fix": With the bug, normally when you attack the bugged, herd attacking nightkin, his/its Stealth Boy never malfunctions allowing you to see it. Also, when it dies, it stays invisible. This is a sign that the bug is preventing completion of this task. But letting a companion (Boone was used in this case) attack/kill the nightkin will make its Stealth Boy fritz like a normal nightkin and when it dies it will become visible. You will have to initiate the attack for your companion and the nightkin to become aggressive toward one another. Loot the nightkin corpse and talk to Dusty McBride to receive 75xp and all the steaks you want from his freezer.
 * Possible Bug "Fix" 2: Try turning the ps3 fully off, flip the switch in the back to totally turn it off, and back on so it clears the cache and resets the event. Wait till that time for him to show up and get near him to start it off. Sometimes works.
 * Possible Bug Fix: Turn the console off and remove the power cable. When you load the game the cache should be cleared. Go to the corral to wait. The nightkin will show up around 00:20. Avoid the temptation to look at or watch the nightkin as this can lead to him getting stuck on the pole by the train tracks. Face the opening in the fence instead and wait to hear his stealth sound effect and the shots of his minigun hitting the brahmin. Once the brahmin is dead you can proceed normally.
 * A similar bug. However, the nightkin appears already at daytime and remains there uncloaked. After you kill him, you're able to tell Dusty McBride that no one will kill his brahmins. You finish the quest and gain fame with Novac.
 * The nightkin will respawn after the mission is completed after some time. At high levels it will be a nightkin master. The nightkin will respawn uncloaked, possibly related to finishing Guess Who I Saw Today. It is possible to complete the quest twice this way.
 * Even though you are killing a nightkin, it will not have any effect on Davison if you have started the quest Come Fly With Me and have not talked to him.
 * If this quest is completed after Come Fly With Me it may reopen the dialogue with Cliff Briscoe about purchasing the souvenir rockets again. After this, if the player waits in the shop, Cliff will disappear from the game.
 * Even after you kill the nightkin, loot the note and go back to Dusty McBride you only have the option to tell him "Not yet." This will hinder you from completing the quest.
 * Bug "Fix": By writing "set "00084223".nChupacabraStage to 20" will fix this bug.