The Uncommon Cold is episode 43 in season 2.
Muriel is very sick, coughing and sneezing while making breakfast. She makes eggs and ends up sneezing them on Eustace, who winds up eating them. As she is sneezing, a slug inside of a green bubble gives a message to the residents stating that him and his companions are slaves to a Big Bayou snake and that freeing them from their enslavement will get rid of Muriel's cold. Courage and Muriel travels deep into the bayou to complete the mission, finding the slugs shackled inside of a cave making stuffed replicas of the snake with its shed skin. It turns out their owner, Big Bayou, is a narcissistic snake who practices Black Bayou Magic, which after the slugs got a hold of his magic spell book, was able to send the cold to Muriel. The problem is, they were able to get a piece of the common cold spell, but not the cure for it. So Courage has to get into the Bayou Snake's lair and get the cure for the cold and find a way to free the slugs. As Big Bayou is bathing in a hot tub a short distance away, Courage uses his tongue to get the Big Book of Black Magic from the window of the lair and takes the book back to the cave where he finds the cure for the cold, which tells Courage to imitate a chicken and lay an egg and have Muriel drink from the egg. Muriel is cured and as Courage is searching for a way to free the slugs, Big Bayou appears in the cave and chases after Courage and the book. Courage goes into the water with the book and looks up a way of making the stuffed snakes come to life and obey his every command. It says that he would need venom from a real Bayou snake, and as he is reading this, Big Bayou appears and starts to bite courage, who uses the book to block the bite and as Big Bayou is shaking the book off his fangs, the venom sprays some of the nearby stuffed snakes and Courage uses this as an opportunity to command the snakes to attack Big Bayou. As Courage is going back to the cave, it turns out that Muriel used her nail file to free the slugs from their shackles. Back at the farmhouse, Eustace has caught Muriel's cold and as he is sneezing, the green bubble appears except instead of the slugs, Big Bayou appears and is shown to be held prisoner by the stuffed snakes and is sending an SOS. Courage lays an egg and grins as the episode ends.
Easter EggAbout 4 minutes into the episode, when the slugs show Courage the spell that they used, revealed amidst the word "YADDA" in the text is a secret message:
"Bambi, you sweet thing. Can you read this? If you could why do you work at CN?"