During the dinner scene, when Beetlejuice tries to get the Deetz to leave the house for the first time, they all (except Lydia) get possessed and start to dance to the Banana Boat Song:
At around 00:53 (timestamp based on the YouTube clip above), Lydia just stands up and goes away. At no point in time does she seem to follow the others' movement. Everyone else seems to be bound to the table, unable to move on their own.
Is this ever explained? Is it because she's "special" (same reason she's able to see the Maitlands)? Or did Beetlejuice cast an eye on her already? Or was this the work of the Maitlands only? If so, how did they learn to summon the hands from the shrimp cocktails?