The Red Sea Sharks: Part 1 - S3-E1
Revealing mistake: When the doorbell rings, Tintin and Haddock go to answer it and Calculus, on his roller blades, stands up and falls back down again. Snowy, under the couch, is peeking his head out and moves back into the couch when Calculus falls. When he does this, Snowy's ears pass through the couch. (00:05:50)