Can I send a reply that only certain people can see?

Yes. If you'd like to send a reply to a select group of participants in a Wave, follow these steps:

1. Open the wave to which you'd like to reply.
2. Click the arrow next to the timestamp in the compose window, and select Private Reply from the drop-down menu.
3. Click (+) to select the participant(s) you'd like to include on your private response.
4. Enter your reply in the text box, and click Done.