The Sosumi is an ancient Japanese fishing utensil: carved to look like a snake, the wooden block helps force fish out of cormorants kept on a leash for fishing. Struck with a goat's horn at just the right place, the Sosumi makes a sound akin to a marimba or a xylophone.
This is just by accident, of course, and has nothing to do with music. Apple's legal department heard this story or one very similar from Jim Reekes when the engineer had to change the file names for new sounds added to System 7 so they did not seem too musical (which would have given Apple Corps ammunition in their quarrel over the name "Apple").
In any event, you can have your Mac play Sosumi when new mail arrives — or any other... noise, of course:
›› Alter the way new mail sounds in Mac OS X Mail.