Nothin' But a Hound Dog

Nothing 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 tell you that something is wrong with him. He will then ask you to go to Julie Farkas, located in Old Mormon Fort. She will tell you that there is a man (Dr. Henry, in Jacobstown) who can help. You must then tell The King that Rex can be fixed. He will allow you to take Rex to Dr. Henry, who will tell you to find at least one dog brain to fix Rex. There are four possible brains to choose from:
 * The first brain is at Gibson Scrap Yard, just north of Novac. Old Lady Gibson will ask you for 700 caps in exchange for Rey's brain. If your Barter skill is at least 70, it can be obtained for free. Or you can perform a sneak attack on Rey and take the brain off of his corpse.
 * The second brain is at a Fiend camp near Poseidon Gas Station, 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. Remember to keep Violet's head intact when you kill her if you plan to complete the quest Three-Card Bounty.
 * The third is in The Fort, to which you gain access in the quest Render Unto Caesar. Talk to Antony about Lupa and eventually about a brain for Rex. Antony will then ask you to give Lupa an honorable death. You must fight Lupa in the arena with only a machete and no armor. Your reward will be Lupa's Brain if you defeat her in a 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 take you to HELIOS One, to gain an NCR guard dog brain with no 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).

It should be noted that you can only choose one.

Behind the scenes
"Hound Dog" is a song written by Jerry Leiber and Mike Stoller and was originally performed by Willie Mae "Big Mama" Thornton. Elvis Presley covered the cover version of "Hound Dog" by Freddie Bell and the Bell Boys.

Bugs

 * 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 conversation with Dr. Henry. It makes this and every other quest involving Dr. Henry impossible to complete without console commands. To complete the quest via console, use the command: setstage 001176B8 100.
 * Stage 4 of the quest contains a grammatical mistake. It tells the player to acquire a brain from one of "Old Lady's Gibson's dogs", rather than "Old Lady Gibson's".