Quote Originally Posted by Alabenson View Post
I think I've seen ponies flick their tails to produce a "snap" sound.

If I'm not mistaken, Rainbow Dash does so when she tells Applebloom that she can get her a Cutie Mark "like that!" during Call of the Cutie.
Remember Fluttershy's nose-boop-tail-thwip thing? That was kinda snappy. ^^