I got a response from one of the agents I queried this week. The subject line was the word "Representation." (Actually, that was the name in the "From" line, but I didn't notice that distinction at first glance.)
Okay, so I knew I'd only sent a query and it was therefore impossible that anyone would be offering representation based on that. But it still made my heart beat a little faster.
The body of the email said this:
Dear Ms. Scott: Thank you for writing to inquire about my interest in representing your project, /Scratching at the 8-Ball/. Unfortunately, I must decline because I cannot take on the work of additional clients at this point. My best wishes as you seek publication. Sincerely, [Agent]