Customize Comment Form Text in Twist of Ten?

Hi. I’m working on a site that uses the Twist of Ten theme, and I’d like to change the text for the comment form to something other than “Leave a Reply”.

I’ve checked in the comments.php file and did a CTRL+F for the word “leave” and didn’t find leave a reply.

There’s a note in that file that “The actual display of comments is handled by a callback to twentyten_comment which is located in the functions.php file.” So, I checked that file and didn’t find “leave a reply” in there either. Does anyone have any ideas where I should go to edit that text?
Thanks.