The man is surprised at the fact that

M: I hate having my teeth filled. It’s not just the pain I hate. I hate the sound of drilling.
W: So do I. I’d rather have a tooth pulled than filled.
M: [2]Teeth keep causing trouble. [1]Why can’t they transplant teeth the way they transplant hearts? They can give somebody a different heart. Why can’t they give him different teeth?
W: I’ve heard they’re working on that. My dentist says they’re working on tooth transplants right now.
M: On second thought, I’m not sure I’d want to eat with some other person’s teeth.
W：[2]Well, that’s not how it works. The idea is to develop a plastic tooth that can be put into the hole where your own tooth came out.
M: Really? What makes it stay there? Do they hook the plastic tooth to the teeth beside it?
W：No. The plastic tooth is made with plastic roots, and after a while the gums grow around the roots, so the tooth can’t fall out.
M: Are you making this up?
W: No! Seriously. Somebody at the Georgetown University Hospital in Washington has been working on it. So far they’ve tried it on monkeys.
M: Well, [3]it sounds like a good idea.