- say -v "Cellos" "Droid"
You can actually type anything in the second part you want to say.
- say -v "Cellos" "Wow, this is really interesting. I did not know you could sound like this."
In fact, you can just type
- say -v "Cellos"
Then keep typing lines of text. To end it, hold down the Control key and press D (Ctl-D).
There are also many different voices you can play with.