Lincoln wakes up late on a Saturday, and is surprised to hear nothing at all. He walks out of his room to find that the upstairs hallway is a wreck. He sees Lana and Lola come out of their room looking sick, and he tries to back away, only to find a sick Lori and Lynn. He continues to back away, only to be pulled into Lisa's room. He finds Leni, Luna, Luan, Lucy and Lisa, who take his temperature to make sure he isn't sick.
When they know he isn't sick, they explain what happened. Lori got the flu and sneezed on Lynn's basketball, causing her to get infected. Lynn went and drank orange juice from the carton so when Lana drank the juice, she got infected due to the germs Lynn had previously released into the carton. Lana sneezed on Lola, causing her to get infected, and the rest were taking shelter in Lisa's room to avoid the disease.
Lincoln calls Clyde and tells him the flu is invading the house. Clyde mourns when he hears Lori got the flu. Lincoln lets Clyde know six of them are fine, only for Luan to sneeze. They assume Luan is infected. When she says she's "snot" (pun intended), she becomes a "zombie" and they throw her out of the room.
Lincoln says they need to leave the house, but Leni says that they should help their family. Everyone sides with Lincoln and grabs a gun filled with chicken soup, except for Leni who does not believe in the flu. They leave and before they make it downstairs, Luna gets cornered and eventually infected. They make it downstairs, knowing Luna got infected and thinking Lucy also got infected. They try to leave through the front door, but the pets are outside and infected. They try the back door, but find more infected siblings. They head to Mom and Dad's room and find them infected, but they also find that Lucy wasn't infected.
Lincoln tries contacting Clyde, but his walkie-talkie is dead. They sneak into Lisa's room for batteries and see Lily is infected too. Lily sends a snot bubble at them, but it misses and it goes out the window. They recharge the walkie-talkie and make it to the kitchen. When Lincoln attempts to open the door, the snot bubble flies in through an open window and infects Lucy who infects both the doorknob and Lisa.
Leni says she's going to stay behind and help the others, allowing Lincoln to escape. Unfortunately, Luna is about to sneeze on Leni but Lincoln jumps in front of her and gets himself infected. He says Leni deserved to be healthy more than he did, only to end up sneezing on her, thus infecting them both.
Now that every member of the Loud family is sick, Clyde, wearing a hazmat suit, brings his food into the living room, which the Louds quickly devour.
‣Run for It - Harry Bluestone, Emil Cadkin [Title card.] ‣Vibe Link (b) - Richard Myhill [Lincoln realizes that the house is quiet.] ‣Search Party 1 - Harry Bluestone, Emil Cadkin [Montage of the spread of the flu.]
This premiered as a part of Nickelodeon's Halloween episodes.
Rita's face is shown once again, although only her mouth and nose are shown. Lynn Sr.'s full body is shown in silhouette, and his eyes are also shown when he's infected.
Before "11 Louds a Leapin'", Lynn Sr.'s full head was shown, but his face was covered by a tissue.
Also, Rita grew eight bangs instead of six that covers her eyes like Lucy's, her lipstick and left earring are not shown.
Leni is the only Loud sibling who didn't believe in the zombie flu infection.
Lori was the first one to get infected and she was the one who made everyone in the house sick one by one by how her sickness spread.
Lincoln and Leni salute with their left hands instead of the right, which is the more typical one used in the military.
Although Lori, Lynn, and Lynn Sr. were casted in the end credits, they don't have any dialogue in this episode despite their moaning and Lori and Lynn's sneezes.
This episode was shown only once in Poland for unknown reasons.
The order in which the Louds get hit and how they get infected with the zombie flu:
Juice Box - When Lynn is drinking orange juice after getting sick, the carton says "0.07% juice, all pulp". This is a reference to how many store bought fruit juices are only about 10% real fruit juice, or less, and the rest is just added sugar and whatnot.
Mother Teresa - At one point, Lincoln mentions the saint Mother Teresa of Calcutta.
This episode has several references to zombie-related media:
Night of the Living Dead - The flashback where the flu went from Lori to Lynn to Lana to Lola was done in black and white, like the original horror film.
The Walking Dead - The zombie flu noises that the Loud family make while they have the flu sound similar to the walker noises. The episode's opening is also similar to the beginning of the comic and TV show, when Rick wakes up from his coma after the infection hits, with Lincoln waking up in bed after the infection hits. When the walkie-talkie's batteries run out, Lincoln remarks that "the walkie's dead", a reference to the title.
Resident Evil - The flu virus infects both humans and animals, similar to the T-virus from the games and films.
The Amazing World of Gumball - This episode is similar to the episode, "The Joy", where Gumball & Darwin got infected from "Richard's Wonder Hug", then become zombies, and Miss Simian has to find a way to stop the problem from Elmore Junior High School.
SpongeBob SquarePants - The infected flu zombies chasing Lincoln and the surviving sisters could be a reference to this show's episode, "Once Bitten".
Call Of Duty - The idea of escaping a closed environment while fighting off a horde of zombies is similar to the "Zombies" mode of this popular video game series.
Shaun of the Dead - Lincoln instructing his siblings to act like zombies in order to escape the hallway is similar to Shaun and his friends acting like zombies in order to head to the Winchester pub.
Talking Tom and Friends - The concept of being a sick zombie is a reference to the episode, "Germinator 2: Zombies".
Ghostbusters - The music played after the remaining Louds get prepared references the song by Ray Parker Jr.
It never occurred to Lisa to make a flu shot to keep Lincoln & the rest of the family healthy despite her high intelligence and having experience with medicine in "Making the Grade". It's possible she didn't have time to make one considering Lincoln and the gang just wanted to leave for safety. She also didn't think of wearing a hazmat suit, which Clyde did.
While it is true someone who is sick can pass on the sickness to someone else with their germs, it is not possible for someone to become infected immediately. The infection will take effect within a day or more, if the victim does not care for themselves quick enough.
When Rita uses the laser thermometer to check Lori's temperature in the flashback, she says she has a fever, but the thermometer clearly says "98.6°", the same degree Leni got from Lincoln, which is technically not a fever, but normal and nearly close to one. A fever is generally 100° or higher.
Leni was next to Luan in one scene, but in the next scene, she is next to Luna.
When Lana gets infected, her eyelashes are missing. The same thing happens to Lola when she got infected.
When Lincoln says 'That's the crisis?', the closed-captions say 'That's the food crisis?'.
When Lincoln says 'Looks like we're going up. Loud, you take point!', the closed-captions say 'Looks like we're going up. Loud, you take front!'.
From the scene where Luna is being attacked by Lola and Luan until the scene where she walks after being infected, her left paperclip earring is missing.
When Luna gets infected, she starts walking from the bathroom door. However, when Lincoln, Leni, Lucy and Lisa act as zombies, she was coming from the opposite side of the hall.
When Lincoln, Leni, Lucy and Lisa act as zombies, Leni walks to Lincoln's room direction. However, when Lincoln calls them to go downstairs, Leni is coming from the opposite direction.
Geo was infected with the other pets but was still in his ball when being infected, so it doesn't occur how he got infected.
It could be that he got infected by the time he was out of his ball before.
Lincoln left his gun in the Loud parents room, but somehow he has it when Lily stands up in Lisa's room.
When the snot bubble is going towards Lincoln, Leni, Lucy and Lisa, Lincoln doesn't have his gun. But when they duck and stand up, his gun suddenly appears.
When Lily stands up in Lisa's room, the background behind her was the hall and the room doors. When she sneezes the snot bubble, the background behind her was Lisa's room wallpaper but when she crawls to the bottle, the background behind her was the hall and the room's doors again.
When Lincoln and the sisters are going downstairs the second time, Lincoln's gun is pointing to the right (viewer's left). When they get to the stairs' foot, it was pointing to the left. But when they enter the kitchen, it was pointing to the right again.
Lincoln's gun disappears when Lucy sneezes on the doorknob.
When the infected sisters enter the kitchen, one of the chairs disappears.
When Lisa shoots at Lola, the chicken soup goes through the car's windshield.
When Luna is being cornered by Lola and Luan, Lincoln shoots ten times but only two "chicken soup projectiles" are seen.
The same thing happens when Luna shoots Luan.
Lola crashed her car by the hall where the bathroom door is, but it was nowhere to be seen when Luna is being cornered by Lola and Luan.
During Luna's first line, the captions say "Lola".
When Lincoln sees the upstairs hallway for the first time it's a wreck, but later when he and his sisters come out from Lisa and Lily's room, the hallway is somehow clean.
When the Louds eat the food Clyde brought them, Lincoln disappears.
In the Latin American version, Lincoln says "112 square feet" instead of "1200 square feet".
In the same dub, Clyde's nickname "Safe Haven" is mistakenly translated as "Haven a salvo", when Haven in Spanish is "Refugio".
Someone getting infected.
Lincoln assuming Lucy is infected, and Lucy saying it's how she always looks.