How do you abandon a reply after you've started it?

[Guest trellis]

I'm sure this is a dumb question, but I started to type a reply to a thread on here, including a quote of a previous message, but I've changed my mind about posting that message and I can't see any way to abandon the post. Every time I try to reply to the thread, the same text that I'd already typed appears. I can delete all the text I've typed, and the text from within the quoted section, but the quotation header remains stubbornly there and I can't see any way to delete it. I want to reply to the thread, but I don't want that quote header in there any more. Help!