When a common cold spreads through the Loud House, Lincoln believes his sisters have turned into zombies.
Lincoln wakes up late on a Saturday morning, 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 the last healthy person.
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.
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.
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.
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.
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", then "Leni" for the next part of her line.
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".