Shaggy’s apology on the top of the train. It’s also enough for the two of them to figure out a plan to stop Archambault from getting away.
Also when Scooby saves Shaggy from falling off of the train.
When Oliverio and Lena are reunited after the gang unmasks Doubleday—it's nice to see that they really do love each other, despite Lena's flirtatious nature and Oliverio getting jealous very easily.
After the gang decides to go undercover as circus performers and Marius is assigning them their roles within the circus, he notices Velma hiding behind the curtains of one of the entrances, obviously scared/nervous to perform in the show—rather than get mad, Marius seems understanding of Velma's fears and offers to have her run one of the snack carts instead of acting as a performer.