A minor one: Robin is such a Nightmare Fetishist that even her watering can is shaped like a zombie. Paradoxically, it's also pretty cute.
Early on, volcano ashes fall on the Thousand Sunny. Chopper is grossed out since they're sticking to his fur, so Robin offers him to take a bath with her later. Envious, Brook asks if he can take a bath with her as well, saying his face is also disgusting because of the ashes. He ends up being depressed because of his own words. Then Robin bluntly refuses, and Brook falls down, even more depressed.
And then Chopper says that he's completely okay with Brook joining them, to which Brook replies "Chopper-san, I love you!"
Nami and Usopp notice that one of the Log Pose's needles isn't pointing at an island anymore, instead spinning wildly. They deduce the island it was pointing to is too dangerous to go to, and decide to ignore it and hide that fact from Luffy. Guess who shows up seconds later, and notices the spinning needle ? Cue Spit Take from Nami and Usopp.
When Z tells the crew about his huge mechanical arm, Chopper is so amazed that he actually imitates him with his bottle of milk. It's as funny and adorable as it sounds.
While the crew is recovering from their first fight against the Neo Marines, they discuss the situation and what to do next. When Robin states that it would be problematic if she doesn't return to her true age, Usopp says that she should be happy to be 18 again, since she's become hotter and cuter. Robin doesn't take it very well, to say the least. Sanji then berates Usopp for joking around while the crew's ladies are in trouble... before doing the same, in his own way: He realizes, much to his joy, that because Nami was turned into a little girl, he'll be able to see her blossom into a young lady again. Zoro is quick to point out how gross Sanji is, leading to yet another argument between the two.