The Dose The Trap Door : Season 1 Episode 9

The Thing Upstairs has a cold, so Berk makes him some of his special medicine. Meanwhile, a 'horrible green gobby lump' comes out of the trap door and drinks all the medicine, with strange results. As Berk drags the little green thing back to the trap door, he finds the creature's mum has come out too - a large yellow lump. Berk, Boni and Drutt all end up with colds.