How do you play a clip backwards in Sony Vegas?
Found it!

You can press the "J" key to play in reverse. Each time you hit the "J" it will jump a full speed up to x4. If you want to jump by speeds of .25x, hold the "K" button and hit "J". While it is play backwards, hitting the spacebar will jump you back to where you started playing, and hitting "K" will stop you where you are.

To adjust playback speeds going forward, you can use the "L" key in the same manor.

To find the exact point where a breath is taken, you place the play head about where the breath starts, then hit "J", it will play backwards for a bit. Hit the spacebar and adjust the playback spot by hitting the left or right arrow, then hit "J" again. Once you are exactly where you want to cut the clip, hit "S" and you will split the clip right there. 

(The arrows will jump one "frame" according to the frame rate of your project, even if it is an audio project. If it is set to 24 fps, it will jump 1/24th of a second forward or backward)