(PhD) Night-time scene. (PhD) The streets are mean. (PhD) The things I have seen. The good, (PhD) the bad, and the in-between. When you dive to prone, you are surely gonna own, PhD (Flopper)! When you dive to prone, it's gonna shake ya to the bone, all the zombies gonna groan, 'cause of PhD! (PhD) The feelin's growing strong. (PhD) So right that it feels wrong. (PhD) Like the chorus of a song. (PhD) Not short but not too long. Slap your body to the floor, everybody needs some more, of your lovin', your explosive lovin'. When you dive to prone, it's gonna shake ya to the bone, all the zombies gonna groan, cause of PhD! (PhD) (Flopper)! Damn straight.
The Perk-a-Cola costs 2000 points and features a dark blue and purple color scheme, though primarily purple. Its icon displays a radiation trefoil emitting shock waves. PhD Flopper completely negates self-inflicted damage; however, the player will still groan and suffer temporary movement reduction when falling down from an elevated area. Another feature of this perk is that when players dive to prone from a height from which they would normally take damage, a 7.5 meter radius explosion is created upon landing.
The explosion is very powerful, with a maximum of 5000 damage at the center of the blast, and can kill zombies with one hit up to approximately round 20. Between rounds 20 to 30, PhD Flopper will begin to make crawlers, and on rounds beyond 30, zombies will retain their legs even in the center of the blast. The perk is made from prunes and some types of chemicals. However, as this is an explosive "weapon", it should be noted that the player only receives 50 points per kill, when opposed to the 60 points that are acquired by using a bullet firing weapon, so using a gun would be advised if the player is going to buy something, such as other Perk-a-Colas. This perk does not seem to work when diving right on top of multiple zombies. It should also be noted when "flopping" that landing on a prone player while diving to prone will cause both players to be downed instantly, so one should avoid other teammates while diving.
Ascension - In the room by Lunar Lander Д (closest to MP5K), with the grenades available to purchase off the nearby wall. Can also be obtained from a Random Perk Bottle by finishing a Space Monkey round without having any machines attacked.
Call of The Dead - In the abandoned second floor of the multi-story building that branches off of the lighthouse. Can also be obtained from a Random Perk Bottle by killing George A. Romero.
Shangri-La - Will spawn randomly in the mines. (changes spawn with Stamin-Up, Double Tap and Deadshot Daiquiri). Can also be obtained from a Random Perk Bottle by killing a zombie monkey as it cycles the power-up after it steals one.
Moon - Spawns on the far right side in the Bio-Dome near the Mystery Box spawn. Can also be obtained from a Random Perk Bottle by either jumping multiple times on the bounce pads or spawning one with a QED.
Die Rise - Unobtainable Easter Egg in the first elevator shaft from the spawn room.
Mob of the Dead - Found on a small boat along with Mule Kick near the dock area as an unobtainable Easter Egg.
Cell Block - Found in the corner of the library, in the same location as the Olympia. Next to the spawn room in Mob of the Dead.
Buried - Available as one of the Persistent Upgrades by taking a sufficient amount of fall damage repeatedly (Note that it does not protect the player from over-cooked grenades or fall damage). Not physically available nor is obtained from a Random Perk Bottle, which is achieved by killing all the Ghosts after traversing trough the mansion.
Origins - Obtained via the Der Wunderfizz machine. Not physically available.
The PhD Flopper machine is very thin, similar to that of Widow's Wine, and is covered in blood. It has a yellow paint job (which later changes to purple) on the front of the machine. There are four levers, from up to down, coloured red, green, white and purple. Under them, a bottle dispenser with a coffee cup in it can be seen. Under that, the words "Flopper PhD" can also be seen. On the top of the machine, the PhD Flopper shield can be seen, with several rods with yellow spheres stick out of it.
The Perk-a-Cola's name is a parody of the popular soft drink Dr. Pepper.
By combining the Longshot and PhD Flopper Persistent Upgrades, the effects will chain and the player will earn the longshot bonus for every zombie killed with the explosion if the player is holding a sniper rifle.
PhD Flopper is made from prunes. The prunes are not a liquid, but in chunks, with some characters complaining about "eating" the drink.
One can see an empty styrofoam cup in the deposit of the machine.
In Call of the Dead and Shangri-La, the color scheme has been slightly changed for the Perk-a-Cola machine.
In Moon, diving to prone will not trigger the explosion in low gravity areas as the explosion is made when diving to prone from a height that would hurt the player and there is no fall damage in low gravity areas.
This perk in the Russian version is "Доктор бумс" ("Doctor Booms").
Even though the player needs to dive to prone to initiate the explosive effect of the perk, one exception to this is when the player goes prone on the Flinger and is flung to the other side, which activates the explosion upon landing.
Similarly, in Buried, a player that goes to prone on a Trample Steam will be flung and will create the explosion where they land.
Its machine model looks different in Call of Duty: Black Ops II: it has a faint glow, whereas in Call of Duty: Black Ops, it is non-luminescent.
In Cell Block the bottles for PhD Flopper retain their older Call of Duty: Black Ops model not featuring the perks' logo around the neck of the bottle. This is corrected in Origins however.
In the initial release of Origins, diving to prone with PhD Flopper and an upgraded staff caused the explosion to deal an additional elemental damage effect based on the element of the player's staff, but this effect was removed in a later patch.
PhD Flopper still stays at a price of 2000 points in the mobile version of Zombies, however the mobile version does not support dolphin diving, crossing off the dive to prone explosion of PhD. The machine also misses the yellow "rays" ejecting from the PhD symbol.
PhD Flopper's main jingle is not heard at all in Call of Duty: Black Ops II due to the only map supporting the machine to be on Cell Block, which has all of its machines play distorted noises.
The distorted noises are actually a variant of the main jingle.
The backing track used for the PhD Flopper jingle comes from a stock track entitled "Studio 42".