The teeth.

One night, Moshe and Sadie, both in their eighties, go to Blooms Restaurant.
Moshe orders just one plate of salt beef, latkes and new green cucumbers.
Then, when it arrives, he tucks into his favourite food. Sadie just sits
there watching him enjoy himself.
Shlomo, sitting at a table nearby, notices that Sadie hasn’t got a meal. He
then gets quite upset when, with plenty of food still left on his plate,
Moshe puts down his knife and fork, removes his napkin and puts it on the
table.
“How mean,” thought Shlomo, “the elderly lady is just sitting there without
any food. Maybe they can’t afford two meals?”
So Shlomo goes over to Sadie and says, “I hope you won’t be offended but I
see you don’t have anything to eat. Could I please treat you to a meal? It
would really make me happy if you said yes.”
Sadie replies, “That’s very kind of you but there is no need to worry about
me. My husband Moshe and I share everything 50/50 and now that he’s eaten
his half, it will soon be my turn.”
“So what are you waiting for?” asks Shlomo.