Inserted a sound, but it doesn't play

[150mph]

Noob question:

http://s21.postimg.org/v20leqi53/Picture_2.png

I inserted a .mp3 in a new slide and the little loudspeaker appears, but clicking it does nothing but create a selection marquee around it. I thought maybe PP'04 doesn't allow .mp3 so I try a .wav, click it, same thing.

I insert the .mp3 using Insert Movie. When I click that, at least I get a little volume button and little Play button and I can play the sound.

Am I not supposed to be able to simply click the speaker icon and PP plays the .mp3? What am I doing wrong?

PP '04, Mac