The scene with the crow in the window. At first it is a case of Mood Whiplash - the crow tries a blindside attack on Arietty but for a stroke of luck, would have succeeded. Then it gets stuck in the window screen, and gets itself literally beaten silly by a fuzzy slipper. It finally flutters away with not one jot of dignity intact.
Homily is so shocked and horrified at Sho lifting her family's roof and replacing the kitchen with the one from the dollhouse that she faints... onto a sofa that Sho puts behind her at just the right time.
Haru's bickering on the phone with the pest-control people, who apparently can't find the place.
Haru's reaction when all the evidence she gathered that proves the existence of the Borrowers is gone. Carol Burnett's delivery in the English dub is icing on the funny cake.
Aunt Jessica's quip in the dub is also quite funny. "Are you sure you didn't find the sherry?" Doubles as Getting Crap Past the Radar, since sherry is an alcoholic beverage and this is a G-rated movie in the States.