how to turn off a music file!

To me this even sounds like a stupid question. I have a file on my desk top of some guitar music I downloaded that I'm going to try and use in a Keynote presentation. It is in mp3 format. It's 5 minutes long. When I double click on it it plays fine on my iMac speakers. But it's not in iTunes its just on my desktop, how do I turn it off if I don't want to listen to all 5 minutes of it? I'm playing like 6 of these files for a friend to pick which music he likes and we don't want to have to listen to the entire songs if when I start them he doesn't like them at all. I don't see any sort of media player so how do I listen to 20 seconds of it and then turn it off!?

Susan