With the Mister Sandman perk, when you are in Sneak mode, you have the option to silently kill any human or ghoul while they're sleeping. No regular XP from killing the target is earned: Instead, Mister Sandman kills give a flat 50 XP per kill. Since killing most targets would award less than 50 XP, the difference amounts to the "Bonus XP" from Mister Sandman kills.
Mister Sandman is performed in sneak mode and by choosing "pickpocket" on an unfortunate sleeping victim. Choosing "pickpocket" pauses the game and brings up a menu with the options to "murder" or "pickpocket". Choose the former to activate the perk. When used, a short murder animation follows with the player character cautiously looking around and slitting the victim's throat, accompanied by a cartoony jingly fanfare.
Possession of a knife or other bladed weapon is not necessary to perform a Mister Sandman kill, even though the kill animation shows the deed performed with a combat knife.
No Karma will be lost or gained from Mister Sandman kills in Fallout 3 (you will lose Karma for killing a person while detected). However, in Fallout: New Vegas you can gain good Karma by killing Benny with the perk.
If an unarmed weapon is equipped when a Mister Sandman kill is performed, it will be worn during the animation.
If the player has the Contract Killer or Lawbringer perks, killing non-player characters with this perk will not cause the victim to drop an ear or a finger upon death (unless you kill them while detected.)
Mister Sandman kills do not affect Reputation as long as the character is [HIDDEN] when initiating the kill sequence.
Also in Fallout: New Vegas, it is possible to gain unlimited amounts of XP from sleeping children. When the player chooses to murder the child, the animation is played and the XP is gained, but the child isn't actually killed, allowing the player to immediately "murder" them again. This can cause a lot of side glitches however from freezing to spawning to other locations without warning. This same phenomenon happens in Fallout 3.
Despite the fact that the icon image shows a kitchen knife the murders are done with a combat knife (although it is performed with a kitchen knife in Fallout: New Vegas).
If the victim gets up during the animation, they will still be killed when it finishes.
During the murder animation, the player stands up. In that instant, the player is no longer sneaking and a normally already hostile character (e.g., a Raider, as opposed to a Megaton Settler) immediately detects the player and awakens. The victim gets up and acts normally (e.g., cry out and shoot at the player) but shortly after the murder animation completes (even though they are no longer in bed) and they suddenly lose all health and fall down dead.
pc It is possible that while murdering the victim, they will wake, stand up and become hostile towards you, however, they will still die after the murdering animation is complete. It seems that when the character being killed starts attacking the player, no damage will actually be dealt by them. [verified]
ps3xbox360pc In Fallout: New Vegas non-player characters killed by this perk may fall through the floor making it difficult to loot them before they fall.[verified]