Nothin' But a Hound Dog

Nothin' But a Hound Dog is a companion quest in Fallout: New Vegas.

Detailed walkthrough
Talk to The King in the King's School of Impersonation in Freeside. Ask him about Rex, and he will explain that something is seriously wrong with him. He will then request for the Courier to visit Julie Farkas, located within the Old Mormon Fort. She will reveal that there is a man (Dr. Henry, in Jacobstown) who can help. The King can then be told that Rex can be fixed, in which he will allow Rex to be taken to Dr. Henry, who will tell you to find at least one healthy dog brain to fix Rex. There are four possible brains to choose from:
 * The first brain is at the Gibson scrap yard, just north of Novac. Old Lady Gibson will ask for 700 caps in exchange for Rey's brain. If the Barter skill is at least 70, it can be obtained for free. Should this option not be taken, Rey's brain can be taken by force, instead.
 * The second brain is at a Fiend camp near the Poseidon gas station, which is built from ruined campers (trailers). This section is populated by Fiend guard dogs, including Violetta, a boss guard dog. She and her master, Violet, must be killed to acquire this brain.
 * The third is in The Fort, to which access is gained in the quest Render Unto Caesar. Talk to Antony about Lupa, and eventually about a brain for Rex. Antony will then ask for Lupa to be given an honorable death. One must then fight Lupa in the arena with only a machete and no armor. The reward will be Lupa's brain, should she be defeated in battle.
 * The fourth is not marked during the quest unless Old Lady Gibson has been killed, in which case Rey will no longer be there, and the map marker will give directions to HELIOS One, to gain an NCR guard dog brain with no extra benefit to Rex.

Choosing to implant Rey's brain will give Rex the perk Faithful Protector, increasing his attack damage (+25 damage). Choosing to implant Violetta's brain will give Rex the perk Unshakeable Tracker, increasing his speed (+50% movement speed). Choosing to implant Lupa's brain will give Rex the perk Blood of the Legion, increasing his damage threshold (+10 DT).

Behind the scenes
Then name of the quest is a reference to the song Hound Dog recorded by Big Mama Thornton in 1952. It was covered by Elvis Presley in 1956.

Bugs

 * When asking Henry to perform the transplant using any brain, the game might crash. This issue is related to timescale modifications, setting the timescale to its default value (30.0) should correct the problem.
 * Rey can occasionally be found outside Helios One when the Courier is attempting to adjust the reflectors. Rey may be one of the hostile dogs at that time.
 * It is possible to stealthily kill Lupa and loot Lupa's brain from her corpse. If she is successfully killed without the player being noticed, Antony may not "notice" that Lupa has died and will still give you the option to fight her in the arena for her brain. If the player accepts, it is possible to obtain a second Lupa's Brain. DO NOT DO THIS. Having 2 of the brains in your inventory will cause Dr. Henry to not recognize that you have the brain at all, making it impossible to give Rex Lupa's brain. To solve this, either revert to an earlier save, or enter "player.removeitem 0013d851 1" in the console, without the quotes. Make sure that you only have one instance of Lupa's brain.
 * If you have already killed Old Lady Gibson as well as her dogs, Rey's quest marker may change positions on the world map either showing up at Novac or Gibson scrap yard. In both cases, Rey's corpse may be stuck inside the ground, making it hard for the player to see Rey's body or even realize that the body is glitched.
 * Old Lady Gibson may spawn at Helios One hostile. If you don't scavenge Rey's brain its body will actually stay out back in the solar field.
 * There is a chance, if you finish the quest by talking to Calamity rather than Henry, that the variable for Rex's brain won't be set in the quest, you'll get the ending for if you hadn't actually transplanted the brain at all. The fix for this is as follows:
 * - Press ~ to bring up the console.
 * - Type: set "001176B8".nTransplantResult to X

(You must type the quotes for this to work in the console)
 * X is one of the following:
 * 0 for no transplant ending.
 * 1 for Rey's brain ending.
 * 2 for Violetta's brain ending.
 * 3 for Lupa's brain ending.
 * That will fix the issue.
 * This can also be used in comparison with the resetquest trick above. If you do a resetquest 001176B8, you'll then have to pick up the quest from The King and do setstage 001176B8 30. Follow the quest through as normal then, and once the quest is over, do the command above.
 * If you're having any other problems, try this command: set "0010d8df".ReceivedTransplant to 1


 * Upon transplanting Violetta's brain Rex's hitpoints may become set at 0/0 making him impossible to heal.
 * Sometimes the player is unable to enter a conversation with Dr. Henry; he spouts "Keep your head down, there could be snipers about" repeatedly. To fix this, see Henry. To complete the quest via console, use the command: setstage 001176B8 100.
 * If you complete the first part of the quest by speaking to Doctor Henry The King may act like the quest "GI Blues" is active and will say "My eyes on the street tell me you haven't paid our mutual friend Orris a visit yet. Until you do, we got nothing to talk about."