Batman Gambit: Dagur "coerced" a trader to lace his spices with infected eel scales and infecting Berk with Eel Pox, knowing that they would send dragon riders for antidote ingredients on Eel Island.
Fake-Out Make-Out: Hiccup and Mirabel convince Casita to let them leave by telling it that they were only planning on making out.
Internal Reveal: It's here that the rest of the Madrigals find out about Dagur and Bruno's kidnapping when Hiccup and Mirabel try to sneak out to check up on Berk.
Mirabel and Hiccup trying to leave, only for their guardians to "ground" them for their safety against Dagur on the warpath is a lot like the Dreamworks Dragons episode "Live and Let Fly", where Stoick "grounded" the dragon riders to protect them all from Alvin.
Hiccup and the other riders heading out for ingredients to an Eel Pox cure reflects the episode "The Eel Effect", with the reveal that Dagur infecting their island as a form of biological warfare being similar to when he used Johann to plant a Smokebreath nest on Berk in "Smoke Gets in Your Eyes" and Vigo planning on causing a Scourge of Odin-pandemic for a Poison and Cure Gambit in "Buffalord Soldier".
Sexual Euphemism: When Camilo claims that they have things to do in the morning, Mirabel sarcastically asks "Oh really? Who?"
