With the Cannibal perk, when you're in Sneak mode, you gain the option to eat a corpse to regain Health. But every time you feed, you lose Karma, and if the act is witnessed, it is considered a crime against nature.
In Fallout: New Vegas, the perk functions the same as it did in Fallout 3, except that it can be acquired much earlier (at level 4 instead of level 12). After consuming 25 corpses, the Courier will acquire the Dine and Dash challenge perk, allowing them to harvest human remains, rather than eat the corpse directly.
There is a fairly long animation each time a corpse is devoured - roughly the time it takes to drink water from a sink twice.
In Fallout: New Vegas, there is a hidden challenge perk tied to cannibalism that is undocumented even in the official strategy guide. This perk is called "Meat of Champions" and in order to gain it, the Courier must feed on Mr. House, President Kimball, The King, and Caesar. After obtaining this perk, whenever eating a corpse, a notice appears on-screen, stating "The essence of champions flows through your veins. When you cannibalize corpses, you temporarily gain Caesar's Intelligence, Mr. House's Luck, The King's Charisma, and President Kimball's Strength."
In the Beyond the Beef quest, when talking to Marjorie, there's a dialogue option that says, "<lie> It's okay. I eat people too. You can tell me the truth." With the perk, the "lie" part is absent.
In Beyond the Beef, when talking to Mortimer about the society's cannibalism, this perk can be used to convince him that the Courier will help him in lieu of a Speech check.
When selecting "Devour," the camera will automatically go to third person and will zoom out. The Lone Wanderer or Courier can not move, look at their Pip-Boy or draw a weapon. However, it is possible to change weapons with the quick-select menu.
A unique dialogue option is gained with Jas Wilkins after receiving this perk.
A re-skinned version of the Vault Boy image, depicting the Vault Boy as a prisoner, can be found on a sign, warning travelers that "Hitch hikers may be escaped prisoners," along the road to Sloan; Northeast of Jean Sky Diving.