I think they are making some sort of eccentric gestures, like "Oh I hope it's yummy" or something like that. The film has so many questionable moments like that, but it's so enjoyable, I just take it as if Neil Simon just was having a ball with it, and the director gave the actors cart blanch to add their own take to each individual moment.
"Great theater makes you smile. Outstanding theater may make you weep."

l've never been quite sure of this myself. l have always assumed Jessica was asking if the butler was blind and pointing out there was nothing in the soup tureen.

"He's Lying."
"Who's Lying?"
"He is." (Points to Butler)